WordPress won't update

Hi all,

I just tried to update my site to the new version of WordPress but it’s telling me it’s unable to do it. The message that comes up is this:

‘Could not create directory.: /home/ruthstok/public_html/wp-content/upgrade/wordpress-3.tmp’

I’ve never had this problem before, so it seems strange that it’s suddenly happening. I get a similar message if I try to upload a visual image to a blog post.

Can anybody advise what I should do?

My site is at https://www.ruthstokes.com.

Many thanks,

Ruth