If you want to uninstall WMP then go to Computer right click on C: /properties. Select Disk Cleanup and then click More Options. Select Windows components and find Media Player in the list. Remove the check from the checkbox and than click OK. Windows will thn remove Media Player from your setup.
To re install do the steps again, this time check the Media Player box and it will be re installed. Just keep in mind that it will probably request the Windows CD to complete.