if your local to the machine.
Pull down the console and type
map x/a
x=game type
a=map name
ie
map dm/the_name_of_the_map
remember that not all map names are the same as their PK3 file
For more info on all these commands, check out my site at
http://www.mohadmin.com
look under guides for Rudedog's complete rcon guide.