level menù

I need a hand, I created a menu for the levels of my game at every level exceeded unlock the next one!
But if I get to level 10 (example) once finished iil unlock level 11, if I go back to level 6 (example) unlocks the 7 but freezes after the other! how do I?

Have a boolean attribute for each level called e.g. "Level7Unlocked?".
Set these to false by default except for level 1.
When you complete a level you need to set the next ones at attribute to true.
On the level select menu when a level is selected, only change scenes if the levels attribute is true.
Hope that helped you.