Adobe Reader XI is a free software and is used to read pdf's.
Adobe Acrobat XI Pro is a paid software used to create pdf's.
If you have Acrobat Pro 9 or later you can upgrade it to XI Pro else purchase the full version of Acrobat XI Pro.
There's no such thing of upgrading from Reader to Acrobat as both are different softwares and Reader is free to use.
You can though use Reader and Acrobat on the same machine.