How can I de-activate a mac device remotely

Question

I already have the maximum allowed five devices linked to my apple ac. One of them is an old and out-of-use laptop that I need de-activate as a device in order to activate my iphone. How can I de-activate the old laptop without finding it and booting it up? Can I de-activate it from my main Mac desktop?

Answer 1

http://support.apple.com/kb/HT1420
If you need to authorize your new computer and are unable due to already having five authorized computers, you can deauthorize all computers by doing the following:
Click iTunes Store on the left side of iTunes.
If you're not signed in to the store, click the Account button, then enter your account name and password.
Click the Account button again (your Apple ID appears on the button), enter your password, and then click View Account.
In the Account Information window, click Deauthorize All.
Note: You may only use this feature once per year. The Deauthorize All button will not appear if you have fewer than two authorized computers. If you need assistance on using this feature, please contact iTunes Store support via email (http://www.apple.com/support/itunes/store/).