1) Navigate to the pgsql folder in the FB installation directory (you may first need to run "cd .." and then cd "PATH/PATH/..."), e.g. cd /"Program Files (x86)"/Winstrom/pgsql
2) Use the "dir" command to check which version of PostgreSQL is installed, then switch to the /bin folder of the corresponding version (e.g. cd 9.3/bin) / On Linux and macOS the directory is located elsewhere — see https://www.flexibee.eu/podpora/dokumentace/instalacni-prirucka/umisteni-adresaru/
3) Command: psql -U dba -p 5435 -h localhost -d centralServer -W
(-U user, -p port, -h host, -d server, -W require password / 7971)
4) select jmeno, user_type from csuzivatel;
5) begin; (starts a separate transaction — if a mistake is made, you can revert using rollback)
6) update csuzivatel set user_type = 'READ_ONLY' where jmeno = "XXX"; (changes user XXX to READ_ONLY)
7) update csuzivatel set user_type = 'NORMAL' where jmeno = "YYY"; (changes user YYY to NORMAL)
8) select jmeno, user_type from csuzivatel; (verify that everything is correct)
9) \q, or Control + D on Linux and macOS (closes the connection)