There are several ways within iTunes itself. If you import songs from cd, the tracks should already be found from the CDDB database. That doesn't work if you don't import the songs originally with iTunes.
If you very slowly double click on a track in the main library window (or playlist), you can rename a track at a time. Also, if you want to alter a whole album, highlight the entire album, right click, select Get Info, and change the artist, album or whatever. It'll alter every track you highlighted to those attributes.