As announced in our the roadmap, UNS 5.4.x is available for installation on SANDBOX network nodes.
What do I have to do if I’m @network_player on SANDBOX?
UNS v5.4.1 will be enforced by a milestone on SANDBOX on block 1,216,800 (~ TZ)
UNS.network delegate on SANDBOX, please update quickly 
To update it, launch this command:
$ sudo docker-compose pull && sudo docker-compose up -d --remove-orphans
What do I have to do if I’m @network_player on LIVENET?
So far, nothing. Nevertheless, the steps taken on the SANDBOX will be the same for the LIVENET within a few weeks if all the tests are conclusive.
It may therefore be interesting to follow these steps.