This might sound stupid and might get closed anytime but can you change your name on the forums? I searched but I couldn't find why...

Yep, go here and follow the instructions.

http://runescape.salmoneus.net/forums/inde...ODE=dname_start

I'm not sure if you need to have 30 posts before being able to change your name. I don't think so.

That link is dead for me...

Go to My Controls -> Change Display Name.

The link works now that you're not a New Member. At a post count of 30, which happened when you made the post that I quoted, you became a Forum Member and unlocked a wider variety of permissions and features. One being the ability to change your display name. You can read about the other new features to you from this tutorial.
http://runescape.salmoneus.net/forums/inde...s&article=3

Yes, you can do it twice every 180 days.
Go to control panel - Change display name.

I don't think you can change it when your a new member, though.