First of all, wrong board. This goes in Help ( Maybe General Discussion? )
To choose a track, first, say /tracklist to see the list of tracks and each track's number.
You should get something like this ( note: your tracks will be different )
The track with the ">" is the track currently in play.
Let's say I want to play on Hydro Plant. To switch to this track, I would say "/settrack 2" without the quotes. This is because Hydro Plant's number is 2.
For changing number of rounds:
Access your console. You can do this by pressing the "~" key ( no quotes. )
Enter this:
$Pref::Server::SpeedKart::RoundLimit = 10;
Replace 10 with the number of rounds you want.