I need to remove a theme that I have installed in my WP from the library, to cha

Hi there,

Is it a fresh install without existing content?

Let me know :)

I do not understand what you want to say. What I have done has been to choose a theme from the library, install it, but it has not convinced me and I want to remove it, and I don't see how to do it.

Do you have any of your own content in the site that you'd like to save?

Let me know :)

I don't want to save anything, I just want to remove the chosen theme in the library so I can put another theme in the generatepress library

That case you can just use this plugin:
https://wordpress.org/plugins/wp-reset/

Keep in mind that it will erase all pages, posts, and media etc.

Let me know :)

ok, so if a library theme is installed, the only way to change it is to reset everything?

That's the easy way. The hard way would be going through the steps here:
https://docs.generatepress.com/article/removing-imported-site/

We always recommend importing sites to fresh installs only.