- version 2017.1 and older —
Settings/Preferences | Editor | Colors & Fonts | Font - since 2017.2 —
Settings/Preferences | Editor | Color Scheme | Color Scheme Font
I found the settings for changing the value of the font size, but it’s disabled.
It’s disabled because it is not allowed to edit bundled scheme. To “enable” it just create your own scheme based on any of the bundled ones (click the “Save As” button next to Scheme Name):
Once you’ve done that you can alter any of the color/style settings.
If you have somehow increased (or decreased) the font size dynamically via shortcut then just use the “Reset Font Size” action. You can assign any shortcut to those actions at Settings/Preferences | Keymap:
You can also call that action directly via Help | Find Action...:
