Have 1.2 on my computer, do I uninstall before installing 1.4 or just install on top of it?
I would do a full uninstall of 1.2 to ensure a clean install of 1.4. In addition, I would uninstall Python for ArcGIS 3.4 as well if it's listed. Keep the Python 2.7 install as ArcMap uses this release. Starting at 1.4, Python was bundled with the executable. Let me know if you run into any issues.
No need to uninstall. ArcGIS Pro can check for updates and upgrade.
How to Apply ArcGIS Pro Software Updates | ArcGIS Blog
True generally but going from 1.2 to 1.4 there were significant changes in the program so a clean uninstall/reinstall is the preferred best practice based upon my experience.
Retrieving data ...