In Windows, I have been using and upgrading pgAdmin 4 since version 3.1. Now, have just upgraded to 4.4.22 version (mai/2020).
What I do is just download the installer (see here) and run it. It will overwrite previous version. The server connection setups I had in previous versions are all kept when starting the new version as well.
All QGIS Projects (.qgs and .qgz) are compatible between QGIS versions, so you don't have any problem in upgrading from 3 to 3.14.
The data (.shp, .tif, etc.) are independent from the GIS software. All these data format are OGC standards, so you can use them with any GIS software and, of course, with any QGIS version.
We have the specs for all versions up 10.6 (SQL, RAM, etc.) I recently tried to upgrade on my desktop from 10.3 to 10.6 and it completely crushed my CPU (64 bit, i7 2.70 GHz 16GB RAM . Needed to get my computer reformatted, probably wasn't related to Esri and more than likely hardware/video card issues
The difference in needed hardware between 10.3 and 10.6 ...