To have a true english interface, you need to have Windows 7 enterprise or ultimate, those editions let you download free language packs through windows update. With home premium, you can switch to an english keyboard layout and date time format etc. but the display language, all menus including start menu and messages will remain arabic, so not the ideal situation.
Your options are:
1) Anytime upgrade to Ultimate, then download and install the english language pack.
2) I'm not 100 % sure this'll work but if you have the time and inclination, you can back up everything on this computer (if this is OEM preinstalled, create a set of recovery disks), then borrow or download an english language Windows 7 install disk, install home premium and activate with the COA key/retail key/whatever key you got with the purchase. Now, this may or may not work so you must be prepared to go back to the original install.
A word of caution- there are hacks and tools floating around that claim to change the language on ineligible editions. Stay away from those, they'll mess up your activation and licensing files.