Gd library install on server..?

Hello Everyone.

I was in big problem from last few days… i read many forums and manuals. captcha code is not working on my website. there is errors on my server (GD library not installed on server). i am new to maintain server so I have read many manuals and forums to fix this i get many solutions but i have not understood properly. so please tell me any one how to install GD library on linux server. i have dedicated server with WHM and c-panel also.