Maybe you try to adjust font size on Unity by right clicking your mouse and select 'Change Desktop Background' but the utility is not there. Its look like Unity had disable it. But there are tools created to control all of the utilities that remove from Unity.
It named 'Advanced Settings'. You can search it on the dash. Install it if it not yet install on your system.
Run it and you will get all the feature that you need there.
Here is some screenshots of the Advanced Settings utility.
01. Search for Advanced Settings on the dash.