I strongly recommend not changing the levels. Changing stuff in mid-tournament rarely does any good. In this case, the following would probably happen:

Team A defeats Team B in level X in the first round.
After that, level X is being changed to level Y.

Team B: "OMG REMATCH WE DID WRONG LEVEL U CHEATER HAX"
Team A: "NO WE BEAT U ALREADY NO REMATCH NOOBS"

And that isn't good for anyone. So keeping your currently selected levels is probably the best thing to do.