I recently purchased an iPhone 4?

I recently purchased an iPhone 4, and I have had problems resetting it. Unfortunately it will not let me reset the phone because it asks for the password of the Apple ID it is currently using. I would like to find a way of resetting or getting rid of the Apple ID it has.

Added (1). Miguel: Whenever I try that it will ask for the password of the profile and it won't let me through because I don't have it. :/

Settings
iTunes & AppStore
Press one the Apple ID
Sign out

2nd option
Back up all your data
Settings
General
Reset
Erase content and rest