The slug is the part of your URL that follows the domain. On the image below, for example, the underlined part is the slug:
Follow these steps to change your portfolio’s URL/slug:
Open your portfolio in edit mode.
Click Settings in the navigation bar.
Choose Portfolio URL from the list.
Write your new slug into the field.
Changing your slug will not affect your domain settings. Also note that if you change your URL slug, your old URL slug will stop working, so don’t forget to update your shared links everywhere!