I have around 17000 tracks and I think quite a few of them are leveled improperly, is there a way to have iTunes do it again?
I have iTunes Match, is this going to cause problems?
Select all your Tracks in your Library cmd+A. Right click on a random track and select Get Info in the menu. You should get a popup with a warning you are about to edit multiple track info. Click "YES". In the popup under Options you should see the volume slider. Adjust to your liking.
I don't see how this could interfere with iTunes Match so you should be fine.
If you're asking about how to normalize all the tracks then go to the Preferences -> Playback -> Enable Sound Check.
Edit: I found a picture.