How to increase editor font size?
Done, you can try this(on Mac): Preferences --> Editor --> Colors & Fonts, in the right side, then click "save as...", this will create a new Scheme, we name it such as "Custom", then all fields become to editable, font, space, color, etc.
Temporarily adjust the font size
Go to Settings (or Preferences in Mac) > Editor > General > Change font size (Zoom) with Ctrl+Mouse Wheel OR Press "Cmd+Shift+A" for mac.
This will allow you to quickly modify the font size whenever you want. However, the font will get reset to the default size the next time you start Android Studio. (The Control+Mouse Wheel functionality will not get reset, though. You only need to do this once.)
Permanently change the default font size
Go to Settings > Editor > Colors & Fonts > Font. Click "Save As..." and choose a new scheme name. Then change the font size and say OK. This will be the default size every time you open Android Studio now.