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.
I was able to trigger a renormalization my forcing itunes to rebuild its library file. Credit to http://www.mcelhearn.com/how-to-rebuild-your-itunes-library/
There should be two files of note in
Quit iTunes, backup both files somewhere, and remove them from
Start iTunes, and observe that all your music appears to be gone.
Go to File -> Library -> Import Playlist, select the XML file, and hit open.
All your music and playlists should come back, and you should eventually see iTunes reassessing music volume.