You don’t, the standard practice when starting development is to pick an engine version and stick with it throughout development and only update point releases IF there is a specific fix you require. I’m sure there’s some way to ‘painlessly’ update the engine but I’d really not reccomend it specially if you are in the middle of development.
If you really really must upgrade to a major version then download and compile the engine into a different folder (so you have both engines) and ‘move’ your changes and project over to the newer engine, making sure to keep backups of both your project and the engine your project uses.