I've got the 2.8w. The upgrade process was very easy and very well doc'd.
Switching depends on what "mode" you're using your X-Carve in. There is a special grbl version you can download which allows you to engrave in manner better suited for bitmap image files. If you're using this mode, then you need to re-load "regular" grbl, which takes seconds.
I use mine in "regular" grbl mode more often than not. This is because the type of cutting I do is vector or line-based.. In this case there is no switch over time provided the laser and driver are still installed.