Click on the cover image which will open the 'Inspector' tab. This will open a number of options. Click on the 'Background' drop down. For this tutorial, we will change the alignment of the cover image.

 While the tool is quite simple and self explanatory, here are detailed instructions:

The repeat buttons will do just that, either use the image covering the whole cover page, horizontal and vertical will only cover a portion and all will tile the image.

The alignment pad. The new image, when added to the cover will be centered relative to the cover page size, however, depending of the size of the imported image, the alignment pad allows the user to select other sections of the image (above, below, left and right).

We have recorded a short video showing all the above in action:
https://screencast-o-matic.com/watch/cYfUo9BIOo

If you want to upload your own cover image, the ideal size is 795 pixels w x 1125 pixels h. - 72dpi.  

We'd also suggest creating a test project to test and experiment with each and every feature of the project editor to fully understand how they work. This way in case something goes wrong, you can just delete the project and create a new one.