Answer
(Fatwa: 894/679=H)
If the hair is very short, then it is necessary to shave for going out of Ihraam; only cutting will not suffice. If the hair is longer than fingertip then one can trim equal to one fingertip. However, shaving the head is afzal (better/desirable), there is no need to wait, whenever you wish you can perform umrah and get halal by shaving the head. Even you can perform the second umrah just after that and get halal by wiping razor on the head. Delaying umrah just for the sake of hair is improper. Allah has granted you chance to perform umrah so you should not miss it. Get shaved after performing umrah whether you have hair on your head or not.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband