There are a few ways to go about it as mentioned above. This is the method I use:
I name my levels "Level1" to "Level71"
I create a global variable that determines which level I am at. Than when the player clicks on the next level button:
Add +1 to CurrentLevelVariable
Go to layout "Level"&CurrentLevelVariable
I also create another variable to store the highest level I've cleared. This is useful as you can create a continue button like many games that will bring the player to the level they have yet to clear. Hopefully this helps a bit.