to test dopjump:
open paintball2.exe
open console by hitting the tilde ~ button (under escape)
write "map jump/dopjump" without the " "
test
Now head to your Paintball2/pball/maps directory and look where is airtime.bsp and dopjump.bsp placed. By doing this you can logically understand how this works and by changing the path (path = the bolded text ^^) to map you download/make.
Hint:copy downloaded .bsp map into your pball/maps directory then do the same as blaa said and replace mapname "newmap airtime" with the name of the file without ".bsp"