1.0.2OTB->1.1.2 how can i restore the iphone ?

i'm working with an 1.0.2 OTB which has been upgraded to 1.1.2 and working
lately, the iphone crashes too many times, and some programs refuse to be uninstalled

i want to restore the iphone (and stay on 1.1.2) so i can have a fresh start

my question is how to do it ? do i need to install something prior to the restore?
will i need to JB after the restore? is there a guide for such action?

i've tried searching the forum, but with no luck

thank you :)

restore 1.1.1 two times
JB+Activate, prep for 1.1.2
UPGRADE to 1.1.2
JB+Activate, anysim 1.2.1u

OR

softupgrade to 1.1.3
anysim 1.3

what about Verginaze before installing 1.1.1 ?

and, isn't there a way installing without downgrading to 1.1.1 ?