Ringfire, what do you mean by "HD"? Blu-Ray? DVDs are not "HD." Are you thinking of the term "remastered"? This improves the quality of video from TV shows by cleaning them up, enhancing colors, etc. But it doesn't make them Blu-Ray quality on their own.

If you have a DVD player these days, most of them will upscale the video so they look better on high resolution TVs. Ditto for Blu-Rays, some Blu-Ray players will upscale them to 4K definition.

There actually was a video format called "HD" (https://en.wikipedia.org/wiki/HD_DVD) which competed with Blu-Ray, but turned into a big flop.

As far as the DVD releases of Classic H50 are concerned, they were all remastered except for the 10th season, which looked lousy by comparison. When it came time for the entire series to be reissued again in a large box, CBS remastered just the 10th season, improving the quality quite a bit. Classic H50 has never been reissued on Blu-Ray.