How do you do this? stretch/shrink audio for new tempo

Got a guitar track, recorded to metronome, at  90bpm.
 
Need to change the tempo to 80, stretching the audio.
 
How do YOU do this?
 
Suggestions?
 

Thanks for the response.
 
But::  cannot redo the recording. One of a kind,....
 
I stretched the audio by 1.125%  (90-80=10 10/80=.125)
And then changed the tempo to 80 for the project.
 
This was easy because of the ratios. But is not so easy for other stuff.
 
I have also accomplished this for other projects by stretching/shrinking and the setting the project tempo from the clip. This often results in twice the target tempo. In the current case this resulted in 160bpm tempo.
 
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I use audio snap lots for adapting natural sounds to project tempos.  I recorded lots of firework noises last Thursday eve.   Cloned the tracks and snapped the each set of stereo tracks to 16, 1/8, 1/4 and whole notes. Then I cut the clips and moved them about to have 7 minutes from the original 25.
 
Started adding Zeta rhythms and drums,.... 
 
Do the fireworks still sound like fireworks after the snap/stretching.  Enough to know what they bees.
 
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I am interested in how others stretch clips and change tempos as needed.
 
And: what algorithm is used to stretch?  Anybody know?  Changeable?
 
Audio snap defaults to not the best/slowest conversion. And I change it every time.  Sure would be nice if AS used presets.

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