Will I loose GB on my iphone?

Hi if I update my phone will I loose any gb cuz I don't have a lot left on it

No. You don't lose gb's when you update. BUT you will need about 2.5 to 3 gb free and empty to install the update. It needs that much room to move around. Once it's done it only uses 713kb's not gb's.
Make an iTunes backup before you do this. Best luck.
http://www.iphonehacks.com/2014/02/install-ios-7-0-4-update-iphone-ipad-ipod-touch.html