Well, I called my host and we figured out the problem -- I had not installed the new theme to the public_html/wp-content/themes directory, but to another wp-content/themes directly I had duplicatively installed one level above. Apparently it all has to be under the public_html directory in order to work.
I became a bit familiar wtih FTP (file transfer program), but it turned out that I did not need to use this. I simply downloaded the desired theme to My Documents in Windows, then uploaded it from there to my host. However, I agree that FTP is an important process to master.
By the way, I find the BlueHost customer support to be outstanding. They not only are patient and knowledgeable, you do not have to wait a long time for them to come on the phone. I have used them three times -- and will doubtless use them more -- and I give them four stars for each effort. Plus they have weekend hours.
Thanks to all. From my point of view, you can mark this string "resolved," although others of you may not yet feel that way.