The following assumes you have an American sgh-i437, not the international i8730. Even though they have the same name, the internal hardware is different. The process is similar, but you will probably have to search in different places to get the right software for your phone. Using the wrong version will brick your phone.
Do a Google search for "samsung odin tutorial". You'll get a bunch of results including some YouTube videos. I don't think there's one for the Express, but you'll get the idea.
Search on xda-developers for "galaxy express root". One of the methods uses Odin and has a download link for a version of Odin that will work on the Express, and the drivers you'll need on the PC.
Look in samfirmware.com for the original Odin loadable firmware for the Express. This will flash the phone back to factory stock.
