Unable to install the latest version of AVG antivirus

Hello to all,
I am presently using an older version of AVG antivirus.
Last night, while surfing through the net, I found a latest version of AVG, which was free.
Now, I want to replace my older version of AVG with this new version, but my system is not permitting me to do so.
Each time I try to load the new version, I get an error saying: 'Error code oxcoo70643', which says they cannot remove existing version.
It is creating a hindrance in the installation of the new version of AVG.
Can anybody help me in solving this issue?
Looking forward to your answers.
Thanks in advance.
