I had like 5 different ways to edit Flash games...
But most of the ways doesnt work anymore so
the last way i had is:
I used to export files with JPEXS to .png
I used Photoshop to edit files, redrawing, sizing etc. *ITS VERY IMPORTANT*
Because photoshop allows you to export file as .png and set Resampling to Keeping the details.
In that way you won't loose original size and any quality of image
You can open "export as" tab with CTRL+SHIFT+ALT+W shortcut
After you export your file you can import it back with JPEXS.
Hope i helped