Absolutely you can upgrade. However, as stated, since the upgrade is subsidized by Dish, it is "leased" equipment, but you are stuck with the owned equipment (at least that is how it was when I upgraded from owned--and I only bought because back then Dish would not subsidize my additional rooms, which they will do today), and you make the 2 year commitment
Today, there is NO financial advantage to "owning" Dish equipment, you pay the same fees every month, but under a different name. The few people who still insist on "owning" their Dish equipment do so on principal because they "don't like being on any contract commitment." The problem is, several people on this forum did the math, and even after a few months AND after adding the ETF (Early Termination Fee) it is STILL CHEAPER to LEASE in most cases, so OWNING costs more money than committing to a 2 year contract and paying ETF if a few months pass. The only rational reason to buy is if you have no other option or want beyond what Dish is willing to subsidize (or perhaps a portable system), and you will have a hard time getting all or close to all your money back (re-selling the owned Dish stuff) on the huge amount you've spent to own because most people qualify for the "FREE" equipment and install, and AFAIK, Dish does NOT do any FREE installs with equipment you've spent a mint buying, so you eat that cost, too. Also, Dish stands behind their installs, not necessarily your DYI install.
But yeah, easy to upgrade from your owned equipment.