Changing BPM

Edit: Brundle posted as I was typing my novella. lol
 
Cool. That helps.
 
So on top of looking up the Tempo View here's what I'd do based on the info you provided (and will also give you some other stuff to read up on if you aren't already familiar with features/techniques).
 
First I would say revert back to the version of the project you had right before you started messing with the tempo change. Hopefully you created a Save As version of the project immediately before you tried all this. Go back to that version and start from scratch (I'm concerened your attempts at changing tempo may have insert unwanted tempo changes so we want to start with a completely clean tempo map... essentially using the original project tempo). If you didn't do a Save As and can't get back to a clean project without losing any other data/mix settings/etc then things might get a little weirder.
 
Follow these steps and tell us what happens...
 
1) Enable Snap with Snap Resolution set to Whole Note/Measure (or quarter note or something else largish but we'll be snapping to measure starts).
 
2) Trim/extend all AUDIO clips so their beginnings and endings all land directly on a Measure's 1 beat. So with Snap enabled you can just drag the start and end times of each clip so the snap to the start of a measure on the timeline. You can even just drag the start of each clip to the very start of the project and trim the ends but that is unnecessary. This is done so that the audio clip/start end times don't get all screwed up when Tempo change style stretching occurs.
 
3) Now select all those newly trimmed and snapped clips > Right Click > "Groove-Clip Looping". You can also just press L when the clip(s) are selected and it will do the same thing. This turns your Audio Clips into "Groove Clips" which essentially means they will stretch with any tempo changes in your project. They are now "loops" (and I think more specifically/nerdily they are "Acidized" files).
 
4) Set your Now Time to the beginning of the project (not sure if this is necessary but I would just to rule out some weird stuff I think might happen otherwise and am not going to test today), double click the Tempo display in the Transport Module, enter your new tempo (and press Enter).
 
Expected results....
 
All audio and MIDI should obey the new tempo throughout the song. Keep an eye on the Tempo display in the transport module. If it changes then you have an unwanted Tempo change inserted at that point that needs to be deleted in the Tempo View. It should however (barring any previous tempo change insertions) just play straight through at that tempo.
 
Note: The audio may sound a little garbled depending on how drastic the tempo change/stretching was. Don't worry this is just the "Online" rendering algorithm (only there for auditioning stretches) and there are MANY ways to improve the quality... the main one (and simplest) being "Bouncing/Rendering" the clip to process the stretching more accurately in "Offline" rendering mode.
 
That is another topic and I won't bother going into it unless you want to keep the audio you have now in the final project and simple bouncing is not correcting the audio glitches. However look into using the "Loop Constructor View" for cleaning up Groove Clips/Loops so they stretch better (and a WHOLE pile of other cool stuff) and definitely look up the "Clip Inspector" and the area where you control/set Online/Offline rendering modes for clips.
 
More importantly though is making sure the tempo change works and sticks for now. That would require some description of what's happening in Tempo View so I'll wait until you post back (if you do).
 
To see the Tempo View, in the "Global" Menus (at the top of the main Sonar screen) select "Views" > "Tempo".
 
The Tempo map will load in the Multi Dock (at least it does for me... it might float for you). You'll see a visual (and editable) graph of the tempo(s) throughout the project and on the right side a text list of all the tempo changes (if you don't see this list then it is hidden but it should be there).
 
You are already reading up on Tempo View so you should be able to figure out what's up just by looking at it so I'll leave it at that (my bass is calling to me... again) but post an update or if you need some help.
 
This is a tricky/confusing aspect of Sonar unless you are used to it.
 
Also recently user Brundlefly posted some alternate methods that I have yet to explore. Otherwise that might trim a few steps from my method above.
 
Good luck.
 
I go bass things now.