Get it here (official Microsoft Office 2013 full Download).
At the bottom of the page is the full download file (Office 2013). Pay close attention to the note just above the download. Does not support side by side operation with older versions of Office. You will need to uninstall existing versions of Office.
As an alternative you can download/install the side by side version (Office 365 ProPlus) that will allow you to also have other versions of Office installed by clicking the “GET STARTED NOW” link.
Some other resources
System Requirements for Office 2013 Preview
Microsoft Office 2013 Forum
Project Professional 2013 Preview
Visio Professional 2013 Preview