Can I renew F visa in Shenzhen Publc Security Bureau?

Hello,

I am going to Shenzhen in February for a 3 months internship. At the Embassy they gave me a 2-month one entrance VISA F, and told me that once I am there I can SIMPLY go the Police (I guess they mean the PSB) and get my VISA F renewed.

Is it really that simple to get the VISA F renewed? How much would it cost (done it directly, with no agencies)?

One last question: do I need to register my Residence (I will be renting a room) when I arrive in Shenzhen with the VISA F? (the Company I will be working with is not being really helpful with bureaucracies!!)

Thank you