In order to unlink a device you must use the Web version of the App.
It is very important that you only unlink those devices that you will not use more with the App.
To unlink a device simply access Settings in the main menu and select the option: My profile.
At the top, you'll see a tab My devices. In this tab you will see all the devices you have been linking, whether they are deleted or not.
Choose the device you want to unlink and press the Delete option, at this point the device name will be marked as deleted. You must click the Save option to have the device permanently unlinked.
Finally, you can log in to another device and if you open My profile again you will see that the new device appears to you.
NOTE: You should be aware that you can install the App up to a maximum of 6 devices, although you can only have as active devices at the same time, the maximum number that allows your license.