How to update an jailbreak jevey sim unlock iphone 4

Hello there
Please help me out by knowing how do i update my jevwy sim unlock iphone 4 & get it jailbreak agin. Also i'm facing another issue with my phone. The batter drains away too fast. From 100 to 0 in 2 to 3 hours. The phone gets heated up sometimes also. What can i do.?
Looking forward to hear from you soon