how to update older server version

we have a server that we had no idea the network guys were not keeping the avast up to date on it. just figuring out that they have not updated the license in it since 2011. it is server version 4.8 and obviously when i try to update it says the license is expired.

im hoping to just buy what i need to get it updated and rolling again being its already configured and running fine just doesn’t have updates on it. any advice is much appreciated. TIA