The UPDATE is correct.
The DELETE is not something you should run. It will delete the xf_user record, but that is only one of many joined tables. For this reason I do not recommend trying to manually delete users with queries. If you want details then refer to the datawriter:
library/XenForo/DataWriter/User.php
The _getFields() function names the 5 core user tables. The _postDelete() function names many more.