You can easily copy any template created with the template tool by going to your Marketing Materials > Reporting & Scheduling page.
From there, find the template you'd like to copy under the Available Templates section. To the right of the name of the template click Copy.
From here you are given a couple of options. You can make an exact copy of the template, or you can choose to have it created as a Starter Template. If the template is one that you believe you'll be using fairly often, you will likely benefit from saving it as a Starter Template.