If you store your Photos library in a location that's part of a cloud service (for example, Dropbox, Box, or Google Drive), your library might be damaged by the syncing process. To see your photos on all your devices, you can use i Cloud Photo Library. i Photo—and Aperture, if you downloaded it—remains on your system in the Applications folder, and you can continue to use it.
When you install OS X Yosemite 10.10.3 or later, Photos is part of the update.
In many cases, if you had a single i Photo library in your Pictures folder, your entire library—including your photos, videos, projects, and albums—automatically appears in Photos the first time you open it.
Your photos should look the same as they did previously.
If you only need your photos and not the organization or edits you made, the original unedited copies can be restored from the Masters folder.
To migrate another photo library manually: Photos can use libraries from i Photo 8.0 or later and any version of Aperture.