Asi, you're thinking of the much older cup and cone setups. Sealed cartridge BB's are a whole other beast. They are a one piece, crimped over setup that you can't get into.

Pstock, I've seen threads here and other links out on the web where some folks just can't accept the idea of "sealed" and have come up with all manner of ways to open up the sealed BB's and re-pack them. But considering that I've typically gotten 7 to 10 years of life from a $25 sealed UN-51 and UN-52 BB's I'd say you can safely ignore them and just make sure the BB shell threads and inner surface are kept lightly greased to avoid any corrosion from water that may get in there.