Editing a .unity3dwebplayer map

hey so, im trying to edit a map from a dead unity game called Critical Strike Portable. i want to rebake the NavMesh and add some extra spawn points for the deathmatch/team deathmatch mode.

suffice it to say i am clueless on how to actually do it though.. so if there is anyone among you that would be willing to help me, i would be very grateful!

if needed i can provide the game itself along with the map in question.