Yes, if you don't need the previous MC installations (after importing your settings from an older MC to a newer MC) it's indeed safe to uninstall them.
However, before uninstalling I highly recommend first running the older MC as an administrator (this is important) and going into the older MC's Options and go to the Startup section and making sure the Windows Startup option is set to Nothing. If you have Media Center and/or Media Server set to start at Windows startup, make sure it's set at Nothing. Running it as an administrator makes sure any Windows startup options are removed, otherwise you might have leftover startup options (which may or may not give off an error when starting Windows, not sure there).
