SI client is a very good tool to keep abreast of the details & latest upgrades for the programmes installed on your computer.
However, in order to delete your account, please fill out the send feedback form, which is available as the last link from the bottom right, stating that you wish your account to be deleted. Please do give your mail id & login details (though if you are logged in then it will automatically pull up), & within a short span of time, your account would be deleted.
Hope this assists. :)