Should I erase all data off my iphone4?

I'm going into the apple store today to trade in my broken iPhone for a newly refurbished one. Apparently all I have to do I backup my files with iCloud and then I can use that to save all my apps and pics and stuff for the new phone. I will have to turn over my phone now, but do I delete eerything first? I know they will delete it, eventually when they repair it, but I would rather do that myself before I hand it over lol. There's nothing bad on there or anything but some stuff was my Paypal and bank info and passwords and stuff so I don't want them to be able to see it but I also don't want to delete everything and then have them inform me that it shouldn't have or iCloud didn't work properly or something:/ should I delete now or let them?

ICloud should solve the problem you have but just in case you could always sync your phone to your computer and back it up there. In terms of should you delete your data before you return the phone it wouldn't hurt but they will do it. If you are sure that you are backed up and are ready to give them your phone you just go to settings > general > reset > Erase All Content and Settings. That should then return the phone to factory settings.