3.7 Evolution

I should know this, but. . .
Can you install 3.7 Evolution on the same device as 3.6.2?
What, remind me, is the best (safe) place from which to download the most recent version?
At this point, almost all my scores, save the most recent ones, exist as two files, carefully labelled "piece3.mscz" and "piece4.mscz." But some still won't--and probably never will--display correctly in 4.