This tutorial will teach you how to change your Menubar icons.
Iconpaper recommends Clean Menubar icons available here.
1. Navigate to :
Now, back up any of the files which you are going to replace (just in case).
To edit one of them, right click on it, show package contents.
2. Open contents then resources and, replace the files.
The image files are stored as .pdf, which you can edit in programs such as pixelmator or photoshop.
There are already some pre-made menubar icon replacements on iconpaper, such as this one.
3. Log out and log back in after making any changes.
Have fun modding your menubar icons!