If the amendment increases your taxable income, you owe the additional tax shown on line 20 of the Form 1040-X. The amount of your original refund does not change (unless the IRS detects a problem with your originally filed tax return independent of your amendment and adjusts your refund on its own). In most cases you'll want to wait to amend until your original tax return has been processed just in case the IRS does detect a problem with your originally filed tax return and makes an adjustment on its own.
