Can Not Change the Template Themes in Appearance

– Approximately three years ago I installed WordPress on our website in: https://www.studiopatrice.com/wordpress/ directory, intending to create a blog in: https://www.studiopatrice.com/blog
– I ran into some installation difficulty (or some other difficulty, I do not now remember) and reinstalled WordPress in:
https://www.studiopatrice/wordpress2/ directory. But, I believe, that did not solve any problems then, so I gave up for the time being on creating a blog
– A year later, I decided to try again, this time putting the blog in our news bulletin: https://www.studiopatrice.com/on-fine-art/blog/. Again I ran into some difficulty (what I do not now know) and again I gave up on the blog
– Fast forward to today – I am told that I can create a new website using WordPress on https://www.studiopatrice.com
– StudioPatrice.com was originally created with NotePad using HTML code over 10 years ago. It now looks outdated, unprofessional and would be extremely difficult and time consuming to modify. I would like to create a new, temporary website at StudioPatrice.com with WordPress, until I can learn how to use DreamWeaver to create a new modified website.
– The Problem: I Can Not Modify the Template Themes! Every time I change the Theme in Appearance on the WordPress Dashboard, I get a blank webpage at https://www.studiopatrice.com/on-fine-art/blog/. And the blog TRIES to appear in the https://www.studiopatrice.com/wordpress/ directory. (I also updated the WordPress software yesterday to the latest version)
– I Now Have the wp-admin, wp-content & wp-include directories in EACH of the following directories:

https://www.studiopatrice.com/wordpress/ (Where the dashboard works)
https://www.studiopatrice.com/wordpress2/
https://www.studiopatrice.com/on-fine-art/blog/

– I believe I should delete the wordpress2 directory
– The Changes I make are only being made in the wordpress directory, but not in the on-fine-art directory (As noted in my webhosting file manager)
– My General Setting in my Dashboard is as follows:
WordPress Address (URL): https://www.studiopatrice.com/wordpress/
Site Address (URL): https://www.studiopatrice.com/on-fine-art/blog/
– Why does the blog, with the updated themes, not appear in the on-fine-art/blog/ directory until I revert back to the original theme (“Twenty Ten”)?
– After I get the themes to work and have selected my desired theme, will I be able to create a new website on https://www.studiopatrice.com using WordPress and have a separate WordPress blog in the on-fine-art/blog directory. In other words, can I have two or more websites and a blog appearing in the WordPress dashboard?