Plugin for changing profile avatar/icon size

Hi!

I can't find a plugin that allows you to change the default size of avatars/icons. I would love to be able to change the size of the profile avatar/icon. Right now the default size is 200 x 150px I would like to make it bigger. As I have understood this, this cannot be changed in CSS, this default size is in the core file and there should not be any changes made to the core file. The way this can be done is to create a plugin, that's correct isn't it?

 

I have not created any plugins before so if anyone could help me figure out how to do this it would be highly appreciated! :)