CTA does not provide a means to edit vector sprites, only bitmap image sprites.
If you have your preferences Texture Editor set to PS then in Character/Prop Composer you can "Launch External Image Editor" to change the bitmap image selected.
If you are trying to modify a vector based (i.e. SWF) sprite, then you must recreate it and replace the existing one.
You can show and enlarge only the sprite/image you wish to modify and use a screen capture (F10) to get an image you can trace over to recreate it.
Note that most RL character sprites are vector and not bitmap.
Jeff
Get my Plugin Manager and TaskNotes plugins for iClone.
Check out EZColors and Other products for CTA/CA. EZColors: the easy way to change Render Styled (RS) colors!
See my CTA Tutorials on the YouTube channel CTAStepByStep