LG Vu CU 920 frozen how do I hard reset this phone

It is possible that the phone has hung up because there are errors in the software. So to reset remove the battery and the memory card from the phone. Using your PC , scan the memory card for any corrupt files or media files with virus- it is possible when they are downloaded from unsafe sites. If so remove or format the card. Now replace the card and battery and switch on the phone. If the phone hangs up then it is confirmed that the software is corrupt and will need a reinstallation. Seeking help from the authorized service /support centre is most ideal. Take estimate and decide.