Need some assistance please

Hello support team.
I'm doing some work for GDIT on gov't project and in my analysis of environments have found some issues most of which I can resolve myself, but there are 3 things I could use your direction on, if you please...

1. May I get specific instructions on how to do the appropriate yum repo update for postgresql as described at a high level on this page: https://yum.postgresql.org/news/new-repo-rpms-released/. I'm running on both CentOS 7.8 and RHEL 7.8 in my 2 main environments.

2. I want to convert to 'dnf' from 'yum' and could use a 1, 2, 3-style write-up of that procedure.

3. Finally, and this is most important of all... my instances of PostgreSQL were at 10.10 when I got here. I have taken them from there through 10.11, 10.12, 10.13, and now 10.14 successfully. However, I just discovered that the DBA/Sysadmin before me did not correctly migrate nor update PostGIS when going from some version of 9.x.x to 10.10 before I took over. I have discovered the existence of PostGIS 2.5 in 2 databases out of all the databases in my instance of PostgreSQL 10.14. What do I need to do, if anything, to ensure they are up-to-date and useable? Please provide a detailed step-by-step.
Thanks in advance!
:)
Jess
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Jesse F. Josserand | Sr. Systems Architect/SysAdmin/DB Analyst
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