Question about Position Advancment

I saw a position for project assistant 4,5,6 ladder. I qualify for the 5. Say after a year I promote to the 6. How do I find out how to move up past that position? Is there a position that’s a 7,9, or 11? Not sure if this makes any sense so please ask me to reword and I’ll try. My quandary is, I don’t want to leave a current (non gs) position to make 20 an hour in a year and be at my ceiling. Thanks. P.S. any past or current Project Assistants feel free to put your 2 cents in on how you liked/ disliked the position, please. (I have a BA in Business Administration but 0 experience on the business side of employment).