Progress is always good. Let's forget about cPanel for this problem, since you have FileZilla installed. There are some useful tools on cPanel, but there's nothing you need there to solve this problem.
I can't give you a solution in the form of "do X, and it will work" because there a) it could be a # of things, and b) I don't claim to be an expert myself. Here are some things to investigate.
1. You say you uploaded your new theme into wordpress/wp-content/themes. So, using FileZilla, log on, and on your server side, point to that folder. public_html/ would be your top level folder, so you should be pointing to:
In a typical WP installation, you'll see 2 folders, classic and default. If you've put your theme in the right place, you should see a third folder, with something that suggests your theme. If you don't see your theme folder there, it's in the wrong place. Using FileZilla, you should be able to get it in the right place.
2. Assuming it's there, in FileZilla right click on your theme's folder, and choose File attributes.... For me, the numeric value is set at 755, which allows Group and Public to read and execute, but not write to that folder. If you're permissions are too strict, you might have problems using the theme.
3. Back to the issue in #1. In FileZilla double click on your theme folder to look inside it. Typically, you should see your theme's files here, such as index.php. You may have put your theme's files into a folder within this folder. If you did that, you won't see individual files here, and that might be the source of your problem.
What is the theme (& web address of that theme?) you're trying to get working?
Where does ../blog fit into your folder structure?
More than likely, your theme isn't in the right folder or the permissions are too strict.