I assume you mean you want to upgrade only some of the licenses on your network multiple license key to version 20.
I can't say if this is possible or not so check that with your local distributor.
However you could look at splitting the network key into 2 keys - one of which you can upgrade.
Or swapping some of the network key licenses over to software key licenses.
Either way I am sure there will be a fee involved but it may be cheaper than upgrading all of your licenses.
One of the forum moderators. Versions 6.5 to 26 Dell XPS- i7-6700 @ 3.4Ghz, 16GB ram, GeForce GTX 960 (2GB), Windows 10 Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11