If your new uploaded theme is not showing up, you should first make sure that you have uploaded it in the right location which is wp-content/themes in your WordPress installation folder.

Sometimes themes are bundled in their own subdirectory and when you extract them, the files don't go into the correct subdirectory in wp-content/themes.

For instance, a theme called mytheme might be incorrectly placed in:

wp-content/themes/mytheme/mytheme

In that case you need to put the theme's files in:

wp-content/themes/mytheme