Does iTunes Match upgrade my songs on my Mac?

Not automatically. You need to delete the songs on your Mac and download them from the cloud in order to get the higher bitrate version. That's assuming 2 things: the Match version is actually in a higher bitrate and Match actually matched your song and didn't upload it from your computer.

Macworld did a great article on upgrading your tracks.

http://www.macworld.com/article/163620/2011/11/how_to_upgrade_tracks_to_itunes_match_fast.html