Rendering Setting: changing to 64 bits using a 64bits PC

the "rendering setting to 64 bits?"  I'm afraid you'll need to explain more about what you mean.

In that context 64 bit refers to the internal representation of numbers for Sonar's calculations. Sonar can us that level  of "accuracy" on either a 64 bit OS or a 32 bit OS and in either its 32 bit or 64 bit versions. Most newer computers have 64 bit CPUs, which in turn will run either a 32 bit or 64 bit OS. The 32 bit version of Sonar will run on either a 32 bit or 64 bit version of Windows, but you cannot run the 64 bit version of Sonar on 32 bit Windows. Using 64 bit rendering only makes sense if you need that kind of accuracy, and the machine Sonar is running on is irrelevant.