Well one thing, are these on stand alone systems, e.g. not under the control of ADNM (Avast Distributed Network Manager) software, as that software doesn't currently support later versions.
Yes if the the license still being valid it is free and can be converted. I don't know how to go about this if it is a multi-license, single license file, etc. So it would be best to contact sales (at) avast (dot) com and ask how the 4.8 license can be converted to work with avast6.
