Switching from Tier4 to Tier2

Hi everyone ,

Most probably I will have job offer which I wont reject and will need to leave my current master.

When applying for Tier2 inside UK , to where should I do it , can I post it
or should I go to London , or can it be in other cities ?

Also when applying as I will I give them my passport temporarily , what should I use as an ID in UK , will I get any temporary paper stating that my passport is in process ?

What should I ask to my employer regarding apply documents ?

many thanks in advance...