I have a petite body but a very big/round face and small head which makes me appear fat and unproportionate. (Photos)

You can lower your hairline with surgery but to understand how it may actually look or to understand realistic expectations, you need to see a doctor in person and have this conversation.
Forehead reduction surgery or hair grafting transplant can both lower your hairline.  It would be in your interest to have a consultation with a doctor and understand your risks and benefits of each surgery.  It would not be fair to suggest one or the other option without an examination or understanding your specific goals. There are issues of scarring, shock hair loss, hairline shape, and many other factors that must be understood.
First, you need to meet with a doctor so you can explain your goals and expectations.  Afterwards, you'll have a better idea as to how which procedure will best meet your goals.

Your forehead looks long for your facial proportions. Have your considered having your hairline lowered?  see below