The uninstall procedure varies with the version of Windows but find it on the Control Panel reached from the Start button (usually at the bottom left of your screen). Make sure you are not running MycoMatch (MatchMaker) when you uninstall.

If you have added your own species, changed species names, or edited descriptions or data, and you wish to retain these changes, the information needed is contained in the files MatchMaker_Added.txt, MatchMaker_Added.dta, MatchMaker_Deleted.txt, MatchMaker_Renamed.txt, MatchMaker_Edited.txt, and MatchMaker_Changed.dta. Contact the authors about the best way to use these files, as there is no automatic process.

In general recent versions of Windows have improved uninstall procedures. If you follow the usual uninstall procedure for the version, you are unlikely to have any problem with the new version of MycoMatch. In fact, even if you do not successfully uninstall the older version, it is unlikely that any leftover files will have will have an effect on the new version.

If you have Version 2.1 installed, try to uninstall it completely before installing a new version. Version 2.1 is from 2012.

When you uninstall MatchMaker Version 2.0 (from 2010), there will probably be files created by the program that are left over. You can remove these manually, although the program will work if you skip this step.

If you have Version 1.31 (or before) installed on Windows Vista or Windows 7, uninstalling that version of MatchMaker might leave leftover files in the folder
C:\Users\username\AppData\Local\VirtualStore\Program Files\MatchMaker\
where "username" is replaced by the name on the account you are using.
Use Windows Explorer or My Computer as in the paragraph above.
 

Otherwise, you can delete any of the following folders (if present):

C:\Program Files x86\MatchMaker\ (just the MatchMaker folder, not the whole Program Files folder)
C:\Program Files\MatchMaker\ (just the MatchMaker folder, not the whole Program Files folder)

C:\ProgramData\MatchMaker\ (just the MatchMaker folder, not the whole ProgramData folder)
C:\MatchMaker_Data\

This is easiest to do with the File Explorer program (formerly Windows Explorer) which you can reach in a number of different ways on each Windows version, if its manilla folder icon is not already on your taskbar or desktop. Holding down the keyboard Start button and pressing the E key should bring it up. The Start Menu can also be used (bottom left of screen or press and release the keyboard Start button). On the Start menu you find it under Windows System (formerly under Accessories which was under All Programs).