Won’t change themes

Hello,

Probably an easy one for you. Difficult for me!
Have default theme up at the moment. I have looked for other resolutions on this forum, but with no luck.

Uploaded a few new themes into theme folder. Including standard themes, such as ‘Open Air’, and ‘Viala”, so they should be acceptable.

Next, they are all showing as ‘Current themes’, under ‘available themes’ page, so they are available.

To change themes, I am supposed to just left click on the new theme I wish to swap, correct?

A little ‘loading bar’ shows in the middle of the screen, the top half of which goes dark grey, whilst the bottom shows a large rendition of the wanted new theme.

I click on the page and the bottom half vanishes, leaving the normal themes page, unfortunately still showing the current default page under the words, ‘Current theme’.

So, I refresh the page and click the ‘Visit Site’, button.
Alas and alack! Nothing has changed and it still shows the old, blue, default page.

What am I doing wrong, please, as I’ve been trying to get it to work for ages, with no luck?

Thank you,

Ray.