If you cannot find it in application options (look for a gear icon in application) then most likely tile content customization is not possible within given application.
This also applies to the Calendar app. Even with the biggest tile, only 3-4 events can be shown and 7 days won't fit*.
There is an alternate way to keep all information like next 7 days from the calendar at hand: arrange desired app(s) on separate desktop (use multi-desktop feature) so you can quickly check this "informational desktop" and return.
The check can be convenienty made using the keyboard. Related shortcuts are
- Win+Ctrl+D to create desktop
- Win+Ctrl+Left to move view one desktop left
- Win+Ctrl+Right to move view one desktop right
So with the calendar permanently open, you can use one shortcut to display it and one to hide it. Of course, the information at the tile (as you requested) could be reachable more easily, but on the other hand, with second desktop you are not limited by space of the tile and you can instantly peek at it whenever you need. You gain flexibility beyond tile view – better view configuration (think about more info apps at the same desktop) and immediate interaction – you can edit displayed week or to do list (or whatever else) right away.
*) Out-of-the-box tiles are keeping certain design rules, including look of icons, minimum spacings or minimum font sizes. In case of Calendar app, I think that displaying of 7 days on a tile would require very small font etc. Displayed among neighboring tiles, such a tile would look like a defaced piece. I think no designer will allow such a thing, and not only in area of user interface design. Maybe some 3rd-party developer can supply an app with ugly-but-extremely-useful tile, but I would not expect this from the Microsoft, they would be going against themselves.