Hi,
You need to hard reset your phone.
Here is a link to show you how. Scroll down to the section "''Performing a factory reset from hardware buttons"''
http://unlockandreset.com/blu-studio-7-0-hard-reset-instructions/
'''Be aware that when you perform a hard reset you will lose all downloaded apps and user data. Your phone will be restored to factory default condition'''
Be patient it takes a few minutes