You can not upgrade Export PDF subscription to Acrobat Pro DC.
However, you can return the Export PDF subscription and can buy Adobe Acrobat Pro DC subscription.Plans and pricing | Adobe Acrobat DC
Please refer the steps provided here to return the subscription: Return, cancel, or exchange an Adobe order
Also, refer this Conditions for Adobe product returns .
If you still experience any issue, you can contact support here contact-bumper
Let us know if you need any help.