Unable to uninstall old Sophos Endpoint Protection from client

I have a client that has a trial version of Sophos Endpoint protection installed.

We have since purchased a licence for EndPoint protection which is a slightly different version to the trial version installed.

I have been trying to uninstall the older version, however the "Authenticate User" option is greyed out.

I have logged into the computer as a user configured as an administrator in Sophos cloud however still no option to Authenticate user. I have also tried uninstalling Sophos Endpoint protection but it states that I must be a Sophos administrator, which I am but it is not recognised.

I need to uninstall this and get the licenced version installed ASAP but cannot do this until the current version is uninstalled.

If I am unable to authernticate the user or disable tamper protection then how can this be uninstalled.

Any thoughts and support on this would be appreciated as the client currently has no security working on it.

Thanks in advance.