Having gone through the VM bereavement process quite recently with a close relative, I can safely say there are parts of the process that are straightforward, and some that can easily result in unnecessary extra hassle.
The process is effectively split in two - the direct transfer of the account from existing customer to new customer, is easy peasy... complete the transfer form at How to let us know if the account holder has died | Virgin Media Community - 4018511 and play email ping-pong with the team.
Any amendments to the package either need to be done via the 0800 number on that page, or via Retentions - depending (in my experience) on how the wind is blowing and/or how competitive the current offers are. The agents who answer the 0800 seemed to be UK-based, but they (at least in my case) were as prone to VM systems failings as any other CS agent, and this can easily descend into chaos without any effort.
It probably is better to do the package change after the account transfer, although there's an implication you can do them both by phone on the same call.