After I originally filed my taxes, I owed $600, and that's now been paid. Now my amendment says I owe $1900. Will my original $600 come out of that?

[DoninGA]

No.  The new amount that you owe is on the amended return, Form 1040-X.  Provided that the amount that you owed from the original return has been entered properly on Line 16.

[fanfare]

The tax is your correct tax. 1040-X becomes your new tax return.

THEN, 

put the amount you have already paid to IRS on Line 16.

If you are revising Estimated Tax, that goes on Line 13.

@kellywalsh357