Pic or catalog number...? Work caboose or SP, or something else?
CheckHERE to identify which one you have.
If this is a basic SP type caboose w/ no screws, then a metal tab punched into the frame at each railing must be bent up to release the cab.
If this is post-1969 with plastic railings, then the railings unsnap at the bottom from slots in the cab, which will release the floor/chassis.