rtriu, I have had the same problems--I have never found a practical way to upgrade. I have tried many times.
[By the way, whatever graphics you tried to put into your post to display, do not work. The one you wanted to display as result of trying this on-line shows up in your post as a big square, with a smaller triangle in the exact center and the triangle is filled in with a light yellow color. I have tried two(2) different up-to-date browsers to view your post with identical results].
I tried to be extra determined on my latest attempt. I spent days and days online, earlier this month, April 2017, trying to do this. I spent an absolutely ridiculous amount of hours. I gave up, AGAIN, trying to do this on-line. I even tried Chat, very time-consuming and the Chat Agent ended up typing in for me 'to call the Sales Team and typed in the phone number'. I did that--it got me NOWHERE. I called Customer Service and after being constantly transferred on April 13 and April 14, 2017--this was hours and hours and hours of being put on hold, being transferred and even being given "a special phone number to a special department" called "Make It Right" Department. I won't include typing in this phone number since it was a non-working phone number. Prior to this last wrong information the Comcast Agent Kayla (not sure of spelling) promised to call me back within 48 hours. I waited --not going any place-for that promised call, with the result of never being called back by her--including right up to this minute!!
I gave up, as I always do. I only try to put this much effort into this goal only every 18 months-2 years. The results are ALWAYS THE SAME.