If you have a real tibia map open it and go to the place where thais is. Open the second map with File, Open (both maps should be saved in the same client version to be able to do that -> Map, Properties, Client Version).
The with shift you can select the part of the map you want to copy, with shift and ctrl you can scroll with your mouse to other floors to select more floors at the same time.
Or if you want to select all floors you can also go to Edit, Selection and click Lower Floors, this way it will select all lower floors if you select a part of the map with shift.
If you selected the part of the map you want to copy, click right mouse and then Copy, then in the second map click right mouse and then Paste.
If you still have problems, post them.