This has been asked many, many times on this and every other photo related forum.
Firstly, it's set at 72 PPI (pixels per inch) not DPI (dots per inch). Some people use those terms interchangeably...but I consider that to be incorrect.
So your images are defaulted to 72 PPI. That only relates to how large they will appear on the screen. The important number to consider when printing...it the size of the image in pixels. You could have an image that is 2400 x 3000 pixels and whether it's at 72 PPI or 300 PPI...it still has enough resolution for an 8x10 print.
Now, that being said...sometimes, labs or even your printer will mess it up when it's set to something like 72 PPI. So I'd suggest that maybe you should change your files to 300 PPI when preparing for print.
My suggestion is to use the crop tool for sizing and getting the right ratio. You can set the crop tool to a specific ratio (5x7, 8x10 etc) and also set the resolution to 300 PPI. Then when you crop, the file will be the right size for the print size that you want.