It's never a good idea to upsize an image. When you upsize an image information has to be created that doesn't exist in order to make the image bigger.
It's always best to rescan or reshoot the image at a higher resolution to get all the data you need.
However, sometimes that isn't possible and you need to upsize the image.
The resize dialog box has changed a bit. For example, the constrain porpotions needed to keep the image from being distorted is now just a chain link between width and height.
Also, I get a preview of my image allowing me to see changes in quaility as I resize. This is helpful to see any artifacts and other uglies I'll be getting as I upsize before I hit the OK button instead of having to go back and undo the upsizing. So, it's easier to decide how much upsizing can be done.
The best part of the new "Image Size" is the way Photoshop CC now does an intelligent job of upsizing!
Now, Photoshop is smart enough to make better calculations of adding additional pixels and keeping some of the details in tack.
Take a look at the example I did of my old barn when I upsized the image with both Photoshop CS 6 on the right and Photoshop CC on the left.
With Photoshop CC, I'm seeing a lot more details especially in the tree area and shadow detail on the barn.
It's looking like a little more effort has gone into the "Image Size" tool to get noticeably better results and the Preview window let's me know how far I can push the resize before the image is beyond acceptable.
So, it's still not a good idea to upsize an image. But, if it has to be done you can feel a little more comfortable letting Photoshop CC give it a shot.