You can absolutely get dtv to upgrade your receivers. And if they try to charge you, tell them to cancel your subscription.
If you do a little research ahead of time, you can basically name your deal if you’re ok being a jerk to them. The way TV, internet, phone and sometimes insurance services work, is your rates rise and services diminish as an established customer and the companies are very successful at getting folks to pay more for less or even more to get more. It’s part of the business plan.
And if you don’t get what you want, including some good promotional rate, switch to dish and get all their free perks and good rate for a while.