To remove an accountant navigate to the 'Users' page, from there select 'Accountants' at the top of the page.

Then, hit the red 'Remove' button. The accountant will be removed immediately and no longer able to share information.

Alternatively, you can select the 'invite' button and invite another accountant, as soon as they accept the invitation, your previous accountant will be removed automatically.

FYI. You can only have one accountant at a time.