UV Mapping Texture File Assignment

[micheus]

... , I realized I wanted a higher resolution file. I tried the create texture feature to make a 512x512 file, painted that file how I wanted it, but now I can't figure out how to assign that file as the texture.

It's easy. First use File->Import image... and load the new high resolution image. Second, find it in the Outliner window use the RMB and select the Pick up Image option. Now, still in the Outliner window, select the material you want to replace the image and with RMB select the Drop picked object and choose the desired option - in this case, Diffuse.
After that, if your old image is not assigned to any other material, you can delete it (RMB on the Outliner window).