Change the "update" button to "upgrade"
While installing Photoshop and Lightroom today, the installation screen showed that I had an existing install of Acrobat DC. I've never heard of Acrobat DC... so I assumed it must be part of the Acrobat system - and I elected to update the installation by pressing the "update" button. Unbeknownst to me, it uninstalled my Acrobat Pro XI and installed a trial version of Acrobat DC. I called the Support Line and waited AN HOUR AND A HALF to speak to a tech support representative to find out how to revert back to my Pro XI. By the time I got to speak to someone, I had already uninstalled the program and reinstalled Pro XI - but missed a dinner appointment with friends because I was dealing with this issue.
I suggest you change the "update" button to "upgrade", as I'm sure I'm not the only one who has been inconvenienced by this.
Apologies for the trouble you had. Acrobat DC won't uninstall Acrobat XI if you are using a serial key for Acrobat XI. Please confirm if you have a serial key for Acrobat XI or you have a subscription.