In the K2 component settings, switch to the "SEO" tab and then scroll to the last section which is "Custom SEF URLs". Enable them and tweak them as necessary (e.g. you can remove the "item" and ID from the URL among other things).

Make sure you're using K2 v2.10.2.

Make sure the category is set as well.

You need to re-navigate your site, e.g. the URL you sent is now: workingtheweb.co.uk/website-hosting-a-definitive-guide