You need to simply download the
latest version of mIRC and run the installer. Close all antivirus programs and any other unnecessary programs and make sure you close any running instances of mIRC. Install the new version of mIRC to the same directory as your current mIRC. Make sure you have all 3 check boxes checked to keep your old mIRC settings.
You should always use the latest version of mIRC, there's little excuse to still be using a version as old as 6.01!
Regards,