When you promote from league level 5 you enter the Super League system.
In the super league the challenge gets tougher. Only top 2 promotes and the bottom 4 relegates. Top 4 will still qualify for Champions League.
The super league has a top level. So no endless level ups. All manager have a chance to reach the highest league level.
The levels are like this:
Premier Division (top level)
Super League 1 (tier 2 level)
Super League 2 (tier 3 level)
Super League 3 (tier 4 level)
... and so on,
... and so on,
When you promote from league level 5 you will start at the lowest current league level in the Super League.
NOTE!
Inactive teams who has not logged in for 2 full seasons will be force relegated to League Level 5 again.
NOTE2!
Sometimes teams go inactive in the higher league. To fill the league system, extra clubs are promoted. That is why sometimes more are promoted than stated above and also why sometimes not all relegated teams actually gets relegated.