Press ~ to display the console, then type "map [level code]" using the following information to skip to the corresponding level.

Level	Code
1	jug1
2	jug11
3	jug9
4	jug16
5	jug18
6	jug8
7	jug3
8	jug17
9	jug10
10	jug19
11	jug13
Deathmatch 1	jdm1
Deathmatch 2	jdm2