There are a number of ways to do this but the easiest way is to login to your ECHOshare account on-line.
Select the Devices tab on the top which shows all of the devices you have associated with your account which have a ECHOshare Agent installed and which have been configured to sync your data.
Then click on the Computer that you would like to wipe clean, and then you will see your documents under the Project Status tab. Click on Select Projects on the upper right which will start a wizard to let you select and remove any project you would like to clean from that particular computer.
If you will not be using this computer any longer, you should disable it. To do this, again select the computer's name from the Devices tab, then select Manage Computer on the upper right, and select Disable from the pop-up menu list.