How can i remove this footer >[Forum create|Invision|Free forum support|Statistics|Contact|Report an abuse] in my site

You cannot remove them all. But, by paying credits, you can remove others except Forumotion & phpbb links.

Like Sanket said, you can only remove some of the links by using credits. The version copyright, report an abuse, and contact links will not be removed.

Even if you were to host a phpBB forum yourself, some of the footer links would still be there. The phpBB link at the bottom is there for every install of phpBB, whether on a free host or not. There are some forum softwares that charge a lot of money for a license to get the branding removed. As far as I know, phpBB has no way of removing that, and forumotion can't override that.

Generally, I've never been that bothered by footer links as a forum user, however. It doesn't detract from the forum experience to have a couple links at the bottom, and a statement like "powered by phpBB" is very typical for all forums. As the others said above, some links can be removed using credits.