Merge 3 games into 1

Hi, quick question:

If I made a game(1 Project file) and i made 2 other similar games(2 project files)- how would i then link them altogether so that they all had the same intro and menu(where you can pick a game) and the same end scene as well?

Many thanks for reading, and more thanks for the replies!! :D

Copy one of the game's layers and events into the other one.

Also becareful of variables and good structures.

Question on this topic what if you have free edition ? can you still do the same still hit past it or would it lock you down