You just need Z4 when you install Z4.2 and for the first startup, that's it. You can safely delete afterwards...I keep personally mine in a compressed folder with a Registry file, just incase I need a quick setup for 4 without the lengthy installation.
"Upon first launching ZBrush 4R2 it will need to be activated. It is not necessary to deactivate or remove ZBrush 4 before installing version 4R2." So it's not necessary to deactivate or remove Z4, but it doesn't matter to Z4R2 if you do. I removed 3.5 when 3.5R2 came along with no issue. As long as the projects and…