Hi,
Its up to you - you can continue to run BeerSmith 1.4 side-by-side with the new version as long as you want. When you are comfortable with BeerSmith 2, then you can go back and uninstall 1.4.
Just for peace of mind, I do recommend exporting your recipes and other critical data from BeerSmith 1.4 to a BSM file and storing it somewhere safe before uninstalling 1.4.
Brad