@zarrath I can't really give you a point by point description, but there is a guide on the RetroPie wiki that teaches you how to make themes. I should point you in the right direction at least.
https://github.com/RetroPie/RetroPie-Setup/wiki/Creating-Your-Own-EmulationStation-Theme
One simple thing I can tell you, if you just want to hide some text to stop it showing up, you can use <fontSize>0</fontSize>. This effectively tells ES to make that element have a font size of 0, so nothing can be seen. You use it like this:
<text name="md_description">
<fontSize>0</fontSize>
</text>
This would stop the description from showing on the screen. If you wanted to move the existing elements, or change their size, you would need to play with <size> and <pos>.
Also keep in mind that you may have to make changes to each theme.xml within the system folders as well as changing carbon.xml, but that would depend on what you want to change.