MyBB Community Forums

I have mybb 1.6.5 and i want to reorder some categories, how do i do that?

You mean you want to reorder how your forums are displayed to everyone or simply reorder how threads are displayed?

For forums go to your admin CP and forum setting and change the forum display order numbers to what you wish.

For threads go to the bottom of post bit on your forum, every user has ability to reorder the threads with many options.