This is not my area of specialty but it is my husbands. All I can say is if you change anything read ALL the fine print. Many mortgages only allow to you pay a bit above the amount you need to pay monthly. Often you CANNOT just pay as much as you want to lower your amount owing faster. So if you change it to a 20 or 30 year mortgage it may very well take you 20-30yrs to pay it off since they want to make all the interest they can off you and make it so it takes that long.

This is something my husband always ensures when we do the mortgage as he likes to pay extra.