If you are getting original images from sites like pldh.net or spriters resource, they will be at a 1:1 ratio.
They do not normally need to be changed in size, just placed into the box with lots of space around it
However, if you do need to change the size, and by distorted edges I assume you mean blurry, then there are few ways to do it, but this is my easy way I found while digging.
When resizing, change its aliasing method from Bicubic Soother (which is Photoshops default one) to "Nearest Neighbour"
Then when changing size, keep it at doubles. ( 25% 50 %100% 200% 400% 800%) And it will stay nice and happy.