Read the following post
printer-template-formatting-tags
From that you should be able to work out how to centre your logo and increase the font size of the restaurant name.
But basically as the last post says <EC> before the logo then <EL> after it - to set back to left side positioning.
Use <C11> for your restaurant name for double font size.
If your printer is going onto another line for item names then consider shorter item names or seperate tags for printing - there are guides on how to do this on the forum - just use the search function.