The brushes should have migrated when you responded "yes" to migrate settings during installation.
Go to the previous version (Adobe Photoshop CC) in the Application Data located here: C:\Users\<User Name>\Roaming\Adobe\Adobe Photoshop CC\Adobe Photoshop CC Settings and copy the Brushes file.
Then go to C:\Users\<User Name>\AppData\Roaming\Adobe\Adobe Photoshop CC 2014\Adobe Photoshop CC 2014 Settings and paste the Brushes file into this folder.