Hard reset on LG Optimus:
1. Turn the power off. If the Optimus is frozen, pull the battery out and reinsert it
2. Hold volume down, home, and power buttons until the reset screen appears
3. Scroll down to wipe data/factory reset (using volume down) and press menu
4. There will be a lot of no's, and one yes. Highlight yes and press menu
Keep in mind, this will erase all of your personal data but will leave the microSD card in tact. Also, it wont work if your phone completely wont turn on at all.
Check out a fun infographic that teaches you how to increase storage, enhance security, improve battery life and clean your device.