You'll have to reflash the ROM. It's not difficult on an LG, but I suggest that you head over to
XDA Forums, find the "development" forum for your model phone (type in lg optimus e - and by that time you should see the phone listed for each carrier that uses it - click yours and you'll be in the main forum for the phone. The Development forum is in there.) People there - who have the phone and experiment with it - can give you links to the ROM image and the program you'll need to use to put it into the phone. Also how to get the phone into download mode. (Usually hold the volume down while plugging in the USB cable from the computer or holding both volume buttons down while plugging it in.)
It's scary the first time you do it. It's boring the 5th time. Some phones are difficult to flash - LG isn't one of them.