how do i cancel my iCloud account completely. . . will i lose any info on my computer

Realize that your "iCloud account" is also your Apple ID and you would lose everything associated with it. Read the next document carefully.

To find out 'How to delete your Apple ID account', click here --> https://support.apple.com/HT208504

Depending upon how much you use iCloud with your computer, it could affect various services even right down to you being able to log in under emergency conditions if you forget your computer password.