Hi Arum,
click the checkbox on the left next to the user name.
Then scroll up to the top of the page and click the "Edit" link.
If the "Edit" link is not enabled, then multiple user names may have been selected. It only works with a single selection. Multiple selection are meant for easier deletion.
If the link still stays disabled with only a single entry being selected, please open a support case.
Kind regards, Niels