LG's default launcher is one of the interfaces which enables the user to change font without rooting or using any other launchers. Change font on LG Optimus G, do as follows:
1. Open Settings application
2. Under Device settings, open Display.
3. Under Font settings, open "Font" and choose one of the existing fonts
4. Tap "Font Size" to change the font on Optimus G, from Small to Extra Large