For this year, you can (and should) still file as married filing jointly.  You should not change the order of the names on your tax return.  The easiest way to do this is to go to your account tools and select "clear and start over"; this will restore your file to its original state.

For next year, you will need to make a new account; you can't change the name on your existing account.  To make the transition easier, you will want to download or print a PDF copy of "all forms and worksheets" from your 2018 return after you have filed.