ClamAV is a renowned anti virus for Linux OS. But, being a resource hogger it consumes lot of memory. It directly affects your server performance.
If you wish to disable ClamAV, simply login to your WHM as root & access option Service Configuration » Service Manager. Uncheck a service to disable it.
Uninstalling of ClamAV can be performed from WHM as well. As a root user cPanel » Manage Plugins. Uncheck the option near ClamAV and click on Uninstall Clamavconnector.