omega where to make changes?
A couple of things you can check...


In your subtheme, have you declared omega as your base theme in the .info file?



name = omega sub theme
description = my sub theme
base theme = omega




Have you enabled your subtheme as the default theme in admin/appearance?
Have you flushed the cache after making changes? ( configuration > development > performance > clear cache )
In dev tools, or whatever you use to inspect an element, when you have the source open, what is the path? Is it definitely coming from your sub theme folder?