Here's the relevant bit from the OFFICIAL NEWS page I linked up there:
"The winner of each stage and the position of each team in the rankings is determined by the following:

1. Higher number of points obtained in the group matches played among the teams in question;

2. Higher goal difference from the group matches played among the teams in question;

3. Higher number of goals scored in the group matches played among the teams in question;

4. Higher number of goals scored away from home in the group matches played among the teams in question;

5. If, after applying criteria 1) to 4) to several teams, two teams still have an equal ranking, criteria 1) to 4) are reapplied exclusively to the matches between the two teams in question to determine their final rankings. If this procedure does not lead to a decision, criteria 6) and 7) apply;

6. Higher goal difference from all group matches played;

7. Higher number of goals scored from all group matches played"