You should read through the what's new file as there are some changes you need to be aware of:
https://github.com/dc42/RepRapFirmware/blob/dev/WHATS_NEW.md
For example:
Important! If you use an IR Z probe or some other type that does not need to be deployed, delete the files sys/deployprobe and sys/retractprobe.g if they exist, because they are now called automatically.
As you are upgrading from pre 1.18 to later be sure to read the notes on upgrading to 1.19. that was the watershed upgrade, after that drag and drop upgrades are single and work with no issues for most people.