Have just completed writing a game using Quest 5.3
If I download Quest 5.4, will this mess up my game? Should I upload the game first?

It will make changes to your game, for some new data types, etc. I'd recommend a good backup before upgrading.

You could upload the game first. Just be sure you save the original somewhere.

Many thanks for your help. Game posted, new Quest version downloaded, and fingers crossed!