Usually, older versions of PowerCore can be removed using the "Add / Remove Programs" option. Should this not succeed, you must manually remove old PowerCore drivers and plug-ins.
Remove from \ Windows \ System32
- pcore.bin pcore.cpl
- pcore.dll pcore.exe
Remove from \ Windows \ System32 \ drivers
Remove all of the included PowerCore plug-ins, which are usually found here:
Program Files \ Steinberg \ VstPlugIns \
Also, it is advised to remove all previous installers unless they are archived in a .zip format.