That would be easy if you can purchase the episodes on iTunes. Of course, if you have a Netflix subscription, you could pay extra monthly for an HD subscription plan, Netflix has seasons 1-3 of the show. Also, there's this fansite (not gonna link it, due to piracy law reasons), which has all the episodes up to date in 720p HD, also he has Save Summer in 1080p.
I did that for your image of Candace screaming "MOOOOOOOOOOOOOOOOOOOOOOOOOOOOM!" at the beginning of Leave the Busting to Us!, HD and without the watermark, I have a Netflix 4 screens/HD plan, which is the highest subscription plan available, so I have access to the HD versions of the first three seasons.
I found there's an option on iTunes in preferences for 1080p downloads, now I'm clearing out my iTunes libraries and downloading the 1080p episodes now that I've changed my preferences. Maybe Phineas and Ferb episodes are worth buying in iTunes after all even though I have Netflix, since Netflix streams in 720p. I'm planning to buy the iTunes 104 Days of Summer collection but I want to find time to save up $50, since you can't purchase episodes individually, you have to buy it all at once if you want the collection.
Saw you edited that line. I did in fact intend to write "six", as I only discovered this wonderful show in early 2009. Also, the page you edited it on was just a temporary placeholder - that copy has since been replaced with my actual article for Issue 137.
Cancelled is when the show stops in the middle even though it was intended to go further. Like, The 7D is planned to have a second season. If something goes wrong (like if Disney decided to shut down forever, which is unlikely) before the second season airs, the show is cancelled, I've heard Flappy Bird got removed from the app store one of the reasons being because someone's brother was too good at it and that guy killed his brother over the game being too difficult, if Flappy Bird was a TV show and it got pulled from air in the middle of the season airing, then that would be a cancellation. If the show ended because it wasn't picked up for the next season and wasn't intended to before it happened, it is just simply ended.