If I amended my tax return from married filing separate to filing jointly can I still e-file my federal return?

Did you already file your original return?  If you did already, was it accepted?  If your return has been accepted, then Yes you can amend your return to change from MFS to MFJ.  You can e-file the amended return.

If you have not filed your original return, then just go back into Personal section and change your filing status to Joint, you will need your spouse's information too.

What do you mean?   Did you already file a return claiming the Married filing Separately filing status?   If so, you have to amend (and file) that return to change it to Married filing Jointly.    If you did not file the original return, you can just edit your filing status and file it now.  

But if you already filed a MFS return, you have to file an amendment to change it to MJS.