This is a long problem for us to do, even just giving you a list of formulae to apply. Post your attempt.
1) Find the premium on the original loan
2) find the balance outstanding after 10 years
3)hence find the total interest payable in the final 20 years
4) find the premium on the revised loan
5) hence find the total interest payable on the revised loan.
6) subtract (5) - (3)