When download the iso i.e. from Microsoft it is possible to use this as full version. It requires to have a valid license code of course. Go with Admin-Rights to the power-shell and enter

Dism /online /set-Edition:ServerStandard /ProductKey:XXXXX-XXXXX-XXXX-XXXXX-XXXXX /AcceptEula

Note that the ProductKey is case-sensitive


It will take a while and require an reboot, after that the Server is activated with the selected Version. Note: It will only work with the same or an upgrade version. An downgrade ie. Datacenter to Standard is not possible