I have been seeing some pictures of people on toribash with big heads, can you buy a big head?
( i know this is a stupid question but i wanna know... )

A big head might be the result of a mod, unless you mean hq big. You can buy a quality 512 head at the torishop

Different mods can mean different sized pieces of the Tori entities. For example, some mods can make the head bigger.

If you are talking about head detail / resolution, there are 3 sizes in quality - 128x128, 256x256, and 512x512. Each have different prices and each show different quality results.

I dont see the 512x512 Head Texture in the market...
Does it change the size of your head or is it better quality?

better quality

Ok, Thanks for the info