Bristol_Jonesey
No version of Sonar installs "over" a previous version.
All versions exist side-by-side and there's very little to be gained by removing earlier versions but you DO risk losing various plugins & shared utilities so the perceived wisdom has always bee, simply install the new version and leave everything else well alone
This is what I have been doing for years. I just keep installing the newest version until I build my next machine. Then I start over and only keep maybe the last version and go from there.
The only reason I didn't have Sonar 7 and 8 installed on my newest machine is because I went total 64bit and just didn't install all those old 32bit plugs.
Right now I have all Sonar X versions install on my machine.