Images not writable

Hi.

I ahve been having some issues with my images on WP.

I am having issues with uploading to my media library (I have posted elsewhere to get help with this), but I am also having an issue using Smush. When I use it, I get an error message that says “public_html/wp-content/uploads/2016/04 is not writable”.

Is this a WP issue, a Smush issue or is it my hosting company?

My site is changed online, I don’t have WP on my computer.

Thanks