I was junior member but now my status is just member. Is there any new rule? Actually, I'm learning a lot of things here and my status isn't important
As Raymott said, changes are simply triggered by the number of posts. When you hit 1,000 it'll change again.
The FAQ explains it all (available from the main forum menu): UsingEnglish.com ESL Forum - FAQ: UsingEnglish.com Members' FAQ
I'm not a teacher, so please consider any advice I give in that context.