disk brake and brake pads size for Aveo 2011

Hello guys,
I'm new to this forum and I'm really desperate to find out the information I'm looking for.
I've recently bought Chevrolet Aveo LTZ 2012, 1.3 multijet 95, 6 gears.
My front brakes make no sound but I've heard that I should change them soon. I'm looking for parts to buy online since a friend is going to change them and my problem is that there are two or even more options for the size of parts. For disk different websites mention 276 and 256mm, and for pads 148 and 142mm.
Can someone please help me out? Is there a website can help me out by searching by vin number(I've tried a few, vin number not found and again all the options mentioned)? If I should provide more details please let me know, I'll do anything just not to have to wait for a part then get a friend here to change it to find out it's the wrong one. :banghead: