Default [Q] How to restore/go back to original set up for Xperia X8

Good day mga sir... I have SE Xperia X8 now bought from a friend (my previous X8 was lost), gotta probz with this,,, especial sa baterry life span nya... kahitm full charge kasi sya di man lang siya aabot ng 24 hours mag warning message na to lobat kaya mag charge na naman ako 9under minimal usage ha). before kasi yung unit ko aabot pa sya ng 2-3 days before mag lobat.. sample i charge ko sa office friday afternoon... pag ka monday ko pa sya ma charge ulit (minimal usage also)... sabi ng owner nito, i try ko daw balik sa origianl ROM nya..

KAso ang problema.. iba na rin kasi kernel nito, ito yung current setting nya:
Model Number=E15i
Android version=2.3.7
Baseband version=M76XXXXXXXX4015
ROM= Delneshin 7.04
Kernel=2.6.29.6-nAa-14
Recovery version= CWM based v.5.0.2.8
CPU info=ARMv6


Gusto ko sana ibalik sya sa original ROM at kernel nya... PAANO... Please help me step by step procedure:

Thanks in advance...