You need to use one of the free third party extension managers. Adobe has dropped support for their extension manager in CC versions.
Try:
http://www.projectseven.com/products/ex-man/info.htm
or:
https://www.dmxzone.com/go/22670/dmxzone-extension-manager-for-dreamweaver/
They are both free and seem to work well. The DMXZone version does require you to register and they will send you marketing material, but other than that they are comparable. I use the DMXZone one anyway personally because I don't mind, but a lot of people prefer the projectseven one since it is less intrusive.