Output Tax

Hi,

I have created a new Tax code Rate 8% by using T.code FTXP.

Later when i checked sales order still my old Tax rate 5% is applying. What i need to do for applying new tax rate in sales order??

Is it enough to create a tax code in FTXP or else we need to maintain it somewhere else in addition to creation??

1) What I need to do to change tax rate in existing Sales order?

2) For new orders which tax rate will apply…New Tax rate or Old Tax rate??

Thanks

Rafi