For Messenger Plus!, it's not necessary to remove the old version, you can install the new version over the old one.
If you want to remove Messenger Plus!, you should go to Start => Control Panel => Add/Remove Programs and look for "Messenger Plus!". If it does not appear, reinstall Messenger Plus! to make sure it was correctly installed.
To use Messenger Plus! with MSN Messenger 7 BETA, you must see this thread =>
Messenger Plus! for MSN Messenger 7 - 3.40 BETA.
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