Welcome to the Apple Community.
If you mean de-authorise computers rather than disconnecting home sharing......
You can't (only) de-authorise computers you no longer have access to.
Your only option is to de-authorise all your computers and then re-authorise those you wish to be authorised. You can do this by logging into your account settings in iTunes on your computer (Store > View My ID) and selecting the option to de-authorise all.
Please note however, you are only permitted to do this once in each 12 month period, therefore you would be better de-authorising your computers before you lose access to them. you can do this from the 'Store' menu in iTunes.