The short answer: prompts can change outfits, settings, lighting, and many visual details — but they can't reliably change your character's underlying body type. That's anchored to the photos you trained with.
What prompts can change
Outfits and clothing
Settings and backgrounds
Hair color and style (within reason)
Makeup, accessories, props
Lighting and overall mood
Poses and actions
What prompts can't reliably change
Your character's body type
Your character's facial structure
Your character's general proportions
These are determined by your training photos. If your training photos showed a certain body type, your generations will keep producing that body type — even if your prompt asks for something different.
If you want a different body type
The fix is to retrain your character with new photos. Open Characters → pencil icon → Change photos and upload new photos. Retraining is free and uses your existing slot — no new slot needed.
For more on retraining, see My AI doesn't look like me — what can I do?