We recognise your point, and allowing "software updates" to allow new releases to be installed via a "patch" rather than only through a full installer is on our roadmap. Unfortunately we've been delivering the IDE - in its MCUXpresso incarnation, as well as the earlier LPCXpresso IDE and Red Suite products - in the current way for a long time now. And providing a patch model of updating requires a major rework of the way the IDE product is both structured and built. And for various reasons, this work has not yet reached the top of our queue for implementation.
In the meantime, we would generally recommend the following flow when a new IDE release becomes available....
Install the new release in parallel with the original version. This allows you to evaluate the new release before committing to using it for your main product development work.
When using the new version, use a new workspace - to keep your new "evaluation" world separate from your old "development" world. You can very easily copy your projects from your existing workspace to your new workspace - for example by checking them out of version control again, or simply using the IDE's Quickstart Panel option to "Import project(s) from file system..." and pointing at the root directory of your existing workspace.
Preferences can also be imported from your existing workspace to your new workspace. To do this run your old IDE installation, and use "File -> Export -> General -> Preferences" to export. Then in your new IDE installation use "File -> Import -> General -> Preferences" to pull your preferences in.
Finally, if you have installed additional plugins into your original IDE installation, then you can also import these across. To do this, from your new installation select "File -> Import -> Install -> From Existing Installation" and point at the "ide" directory within your original IDE's installation directory. [Note that on Mac OS X / Linux - this option will effectively run automatically the first time you run the new version of the IDE.]
Regards,
MCUXpresso IDE Support