Well is it a rented server or are you running it on your PC?
If its a rented one, ask the person you are renting it from for help. If its from your PC copy and paste the map you want on the server into the maps folder of where you put the dedicated server(Ex. C:\Soldat\SoldatServer\Maps) then edit the maplist.txt to have the name of the map you want with out the .pms(Ex. ctf_Laos)
