This is a (very crude admittedly) way to achieve tempo changes if you are still looking a month and a half later. I had a song that I wanted a bunch of different tempos throughout so I saved parts of the song at its given tempo as an individual song. Basically, I would end up with a bunch of sections all cut up. Then I export them all as sound files, create a new track and line them up. If you only have 1 tempo change you would need 2 parts of the song saved separately, one at tempo 1 and one at tempo 2.