There are console commands for changing the game mode on the server and which map you play on. All maps can be played on in any game mode, though certain maps are more suitable to play on for a certain game mode.
To vote for a game mode change, type into the console:
vote set sv_gametype 0/1/2
0 - Free for all
1 - Team Death Match
2 - Capture The Flag
To vote for a map change, type into the console:
vote changemap *insert map name here*
After typing in "vote changemap " a list of maps should appear which you can then choose from.