If you have a separate event sheet called vars and make a global variable called Level(Note, you can have the variable on any event sheet, Its just tidy to have some variables on a separate one, As there global any event sheet can access them)
Then on the Event sheet for the level/game, for example level1:
Depending on your set up for leveling do something like this:
Player.OnCollision with (EndFlag)
-> System.addTo(Level, 1) // Adding one to the level count
-> System.GotoLayoutByName("Level"&Level) // Here were refencing the level variable, So if the level is 7 were basically saying "Level"&Level(7)
Do you understand? or do you need me to knockup a example?
If you share your capx, or PM it to me, I'll add it to your game for you, Or i can make a example to show you.