You don't necessarily need to pay for the $25 membership. You could manually rank up to Jr member without paying for anything. The $25 membership just exists for those who don't want to spend time in ranking up but instead want to go the shortcut route.
How do I rank up? Just keep posting?
Posting with constructions and helpfulness in your posts. If your posts bring benefits to the others, you will receive merit for your contributions.
Up
It is considered as bumping post. As per unofficial rule, it should be deleted. You did not make another bump post after that one but because of there are more posts after that one (from other users), your bump (up) should be deleted.
13. Bumps, "updates" are limited to once per 24 hours per thread. Bumping multiple threads at the same time is allowed if it's not annoying. [2][e]
21. Old bumps should be deleted. [2]