aspguitars

Hi! all. I'm new to the site and need some advice. I've just bought a 2001 C220 Diesel Estate Auto. I got it fairly cheap, but it does have some problems. The first is the SRS light stays on. I was told to check for connections under the seats for pressure switches. I was going to disconnect the battery just to be safe, but I've heard that the W203 uses a CANBUS system that doesn't like the battery being disconnected. So how would I change the battery? Also I don't seem to have any kick down. I can change gear using the tiptronic gear selector and this works fine, but can't seem to get it to change gear on the accelerator. Again I was told that this could be the Mass Air Flow Sensor, but this was only changed last July so surely it can't have gone again that quick. As I say I'm new and am still finding my way around the car so any help wold be gratefully accepted.
Thanks
Ade