i want to change my region but i have balance that i can't spend

Here's a couple of ways to choose from:

(1) You can purchase an item that costs more than your balance

and use a payment method for the rest.

or

(2) You can ask iTunes to just zero your balance for you, losing whatever money makes up the balance:

ie: Start with the "Get Support" link at the bottom of their web-page (link below):

iTunes - Official Apple Support

Then choose Apple ID,

Then there'll be a list of options to choose from .. choose the one nearest to your request.

All the best :-)