Hi Brittany,
Can you kindly confirm if you also renamed the pictures after you edited them in Paint? If you didn't rename the pictures (which means you kept the same filenames the original Little Reader pictures had), I suggest that you try doing the following:
1. From your Start menu, go to All Programs
2. Open the "BrillKids" folder, and then the "Little Reader" folder
3. Click on the item named "Open Media Library" and this will open the folder where your Little Reader lessons' media files are stored
4. Open a new Windows Explorer window and open the folder where you saved your edited pictures
5. Select all your edited pictures and "copy" them, then paste the files into your Little Reader Media Library folder
6. When asked if you want to replace / overwrite or rename the files you're trying to paste, please choose to "replace / overwrite" and this way your edited files will replace the corresponding files
Once you're done, open Little Reader and try playing any lesson where your edited pictures are used (or you can simply preview the word/s) and you will notice that the edited files you placed in the Media Library folder have replaced the original ones, so you do not need to add your edited pictures manually anymore.
You may do the same steps above in case you plan to edit a few more pictures next time -- kindly note that this will work correctly only if you keep the same filenames for the pictures. Otherwise if you renamed the pictures you edited, you will need to add them back to each word in LR.
I hope this helps!