boot loader locked

Nov 14, 2012
i have a SE Xperia Arc S Lt18i currently updated with ICS 4.04, build number 4.1.B.0.587 and i want to have a jellybean for my phone but the bootloadeer is not allowed to unlock the phone. what can i do to have it installed with jellybean? btw i am a new member of the MIUI. thank you!