Generally, I would place a folder for uploaded images f'rinstance in the wp-content folder, but that's just me. Others would probably place it in the root WP folder (the same place as wp-admin etc. folders live).
So using either your ftp client or your cpanel or however you access your site to change things, you'd look for something like public_html/wordpress (or whatever the folder WP is installed in is named)/upload; or if you're like me, public_html/wordpress install folder/wp-content/images (my image upload folder). Once you find it, you need to see what the permissions are currently set at (most likely 644), and change that to 666. If 666 still gives you an error message, then you'll need to change it to 777.
If changing the permissions isn't an intuitive thing with your host (some aren't, believe me!), then you should email your host support staff and ask them exactly how to accomplish the change.
Don't apologize for basic questions. We all asked 'em at some point!