Menu bar is topic created by theme widget. To edit it, you should go to topic list and search for categories-icons. Click edit button to open it and set up new content.
The best option for edit is source code editing. This way, you will not delete topic structure.
New window will be open, on screen shown sample to be edit
You may also use build in tools, but need to be carefull not to delete structure. To use tool, click on link you would like to edit, new icon will be highlight.
Click on new icon, pop up window will be open, change values according to your needs.
Save before exit topic details.