V6 will issue a request to uninstall V5 if it is discovered on the system. At this point you should uninstall V5.
To determine if V5 is on the system it looks for 3 files in folder c:\program files\updd - tbupddwu.exe, dcu.exe and aidaemon.exe.
If for any reason any of these files exist after uninstall you may need to manually uninstall V5 as described here.