Help with Bernat Pattern - Softee Baby - Baby Shower Booties

I'm a beginning knitter but just finished my first pair of baby shower booties using the Bernat pattern. They were a huge success...such a huge success that a girlfriend of mine wanted to know if I could knit a pair for her. Trouble is, I don't know how to increase the baby shower booties pattern into a grown-up booties pattern. Any help would be greatly appreciated! My girlfriend is very ill, in and out of hospital frequently, and these would make a fantastic "get well soon" gift for her, besides keeping her feet warm in the hospital.

Thank you in advance!