If you are a manual RU user, please follow these steps:
Go to 'Properties' and simply click on the 3 dots alongside the property you wish to remove, then click on 'Delete':
Please bear in mind that this will disconnect the property from the channels that you are connected to. However, it will not delete the property in the sales channel. In order to delete the property in the sales channel, you need to contact the channel to request it. You can find the contact information for each channel in the following link.
If you are a PMS user, you would need to delete the property on your PMS and the changes will synchronise on your RU account.