You can also download the software from Canon. Maybe it bit more work. On the other hand, you can choose what you want and what not. And, online is always the latest version of the software
No, straightly speaking you CAN'T
In order to install online updates you'll need to have the original Solutions Disc (actual disc or ISO image) in place
Well, actually, you can. It does take a little more work. Keith at Northlight provides
instructions. Basically, you either spoof the Registry (Windows) or delete a file from a duplicated installer package (Mac), which 'tricks' the installer into thinking you've already got Canon software installed. In spite of the check for previously installed Canon software, every updater is actually a full install.
But of course, you can only update as far as the latest available download from Canon, and the newest cameras usually ship with a version of DPP than is later than that, a version not made available for download until a newer update is released.