This is how you can de-activate an administration in Mifas Online:
1) Login to Mifas Online, using the login details known to you. https://services-web-mifas.agrovision.nl/V1/Login/Login
2) Click on the Administrations tile, and at the administration you want to stop, click on: 'Deactivate'
The administration is saved in this way, but no longer counts towards the number of administrations in your license.