Compatibility an issue?

I bought a copy of Norton 360 (15 month edition) at a Staples store but I have Norton 360 Premium edition on my computers at home. My subscription isn't due to expire until March (2 computers show a March installation & on the 3rd computer I installed it when I got the computer in July). What will I have to do to install the new code (it didn't come with a disc, it's a download edition) when my renewal comes due? Simply type in the new code?