Visa extension, where should I deal with it

Hi!

I am searching around the internet but can not find any infos about it. The problem is: i want to extend my entry permit in china. And was wondering if I can do this at any PSB?! Where do i find out the closest one for me might be?! I will be in Getu Valley or 格凸河 (Getu He) in Guizhou Province in the South West of PRC.

Do you also know what kind of documents are required and how long it takes?!

Best wishes, lisa