After downloading the new file, run it to install ZBrush to your computer. Do not install it to your existing ZBrush 2 folder! The new ZBrush 2 folder will contain two executables. Simply run the one that's labeled for 64-bit operating systems. ZBrush will automatically use the license file from your previous 32-bit installation.
Are you sure you’re not leaving something out? It certainly did not automaticly use the license from my previous installation, instead it asked me to activate again, which I tried and got an error on my POP code.
Is there a specific place the old install needs to be in order for the new version to find it?