You can go to FEUP through four bus lines: 204, 300, 301 and 803. More info about Porto Bus services at STCP and Itinerarium websites.
By Train
If you arrive at Campanhã station, you should take the metro and choose one of the following lines: A (blue), B (red), C (green) or E (purple). You must change trains at Trindade station and take line D (yellow). You should follow the directions in the “By metro” option above.
If you arrive at S. Bento station, take metro line D (yellow) and follow the directions in the “By metro” option above.