1. Open the terminal and run one of these commands:

sudo rm /var/lib/apt/lists/lock

or

rm -f /var/lib/apt/lists/lock

or

killall -9 apt-get aptitude

Then make an update with this command:

sudo apt-get update

2. Also, If you receive this error:

E: Could not get lock /var/lib/dpkg/lock

Via the terminal, run this command to unlock it:

rm -f /var/lib/dpkg/lock

Then update with this command:

sudo apt-get update

credit : http://www.upubuntu.com