To add or remove Primary Tags select / deselect the checkbox buttons.

To add Other Tags use the autocomplete and start type in the tag you want to add, then select it from the autocomplete list.

To remove an Other Tag, find it in the list of tags to the right of the autocomplete input, then click on the small x in that tags button.

To create and add new Other Tags enter the Tag you want to create in the New Tags input box and kit the enter key.

Once you have made all you changes, click the Save Document button.