Open the relevant object, and click the 'Archive' button. However, archiving an object can only be done when certain requirements have been met. So, before you try to archive an object, check the following list:

The object cannot have any future reservations.

Move all existing reservations for this object to a different object, and create a block to avoid any new reservations from being made. Edit the object to do this.
Read more: Blocking an object for new reservations

The object cannot have an active setup.

Once the object does not have any future reservations anymore, you can remove it from active rent by ending the current object setup without adding a new one.
Read more: Remove an object from active rent

The object cannot be part of an active owner agreement.

Open the object, and check the 'Owners' tab for any agreements. If there is still an active agreement, edit it to add a specific end date.

The object cannot have future tasks assigned to it.

Any unfinished tasks related to this object must be deleted or finished. Open the object, and check the 'Todos' tab. This will take you to an overview of all todos for this object in the Todos module. Use the checkbox at the top of the list to easily finish or delete all todos of this object.