if you use the old WAS 5.1 runtime in RSA 7.0 then be careful when you migrate to RSA 7.5 because there doesn't exists a support for WAS 5.1. Further if you use the modeling perspective of RSA 7.0 you should check after the migration of your projects in RSA 7.5 that the formatting of your UML-element documentation is alright. Check further if the layout of your diagrams is ok. I'don't say that the migration doesn't work, I just say "check it".
RSA 7.5 will require you to migrate several of your projects. My tipp is that you create a baseline on your projects before you do that step and after the migration is completed you compare the changed files with your files of your baseline.