tempo changes more questions

good morning everyone, question, how does one change the tempo of a song somewhere in the middle of the song? what i' trying to do is start the song at 80bpm then somewhere start increasing the tempo to 100bpm then back down to 80.
does that make any sense?
thanks so much 
 
ok, I followed the directions on the link provided by SCOOK however what happens when I enable groove clip looping (this is a guitar audio track) it becomes out of sync with the midi drum track (EZDrummer)
then if I try to change the tempo of the audio track WITHOUT enabling groove clip looping it has no effect.
i'm missing something, as usual, what i'm trying to do is start a song at one tempo, speed it up then low it down
thanks so much again for your help  

What I am currently doing is setting the Now Time at where I want my first beat to be, right clicking on the lower half of the time ruler, selecting Set Measure/Beat at Now (then enter the desired measure/beat number). This sets the first beat... then I move the Now Time further along the ruler and repeat the process so the beats line up where I want them. This shows up in the Tempo View. You can also just draw or type in tempo changes in the Tempo View which is probably easier if you are starting with a fresh project.

Hey, scook... do you know if there is a way to use that tempo change function with the various Audiosnap algorithms instead of the default Groove Clip one? I'm still trying to figure out an easy way to fix these tracks but I'm starting to think I may have to do it all manually. I'm willing to do it but it's gonna take forever. Cheers.