The templates are usually 300 dpi.

Any of our product that are 8×10" can be printed up to 16 × 20" without it looking pixelated. A product that is 8' x 12" can be printed at 16 x 24". Or you can crop off the edges to make it any size. 

What I would recommend is up-sizing in Photoshop before printing it. In Photoshop you would go to the top menu and click on Image>Image Size
 then make it the size you want then click Ok.

Depending on the product though you might need to crop the sides to print at a different size. Also your photograph will need to be high quality at the larger size. When printing smaller than 150 dpi, ask your print lab about the results for their printer.

I made the video below to help answer this question

Additionally, this video by Pete Collins is a very helpful explanation of Photoshop CC's up-sizing abilities.