Upgrading ETC ION version

There should be no problem with your showfiles. There might be some aspects of effects that can behave a little different in cues, but in general the showfiles are absolutely compatible.
Because you have about for or five years worth of development added your console, I suggest reading all the release notes of the versions in between. The important ones are 1.9.5, 1.9.8, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5.
You will need new keycaps because some buttons changed their label. I would suggest you download the current release version from the website (version 2.5) and then call the hotline so they can run you through the updating and also get the process for the keycaps started.