Thank you for letting us know about this question that you have in mind.
For you to deactivate or to remove the computers that you no longer use, you may login to your Trend Micro MyAccount online. Once logged in, you can just click on the "x" button over the device that you would like to remove. Please see the figure below:
Figure 1. Example list of devices in Trend Micro MyAccount.
You may click here for you to login to your Trend Micro Account.
Should you have further concern, please do not hesitate to reach out to us.