Old category slug will not completely delete

I am trying to tidy a category slug which, because of a now-deleted one of the same name, is hyphenating with a number on the end.

For example, I created a normal category called ‘shop’, then created it again using the Tribulant eCommerce Checkout plug-in. I then deleted the first one, but noticed that this plug-in category is called ‘shop-2’.

How can I remove this hyphenation, so that the category slug updates to appear as ‘shop’? I can understand why it is hyphenated if there were multiple versions.

Thanks,

Spen