Photos app - There is not enough disk space to migrate your library
I have Macbook pro late 2014 with retina display.
I have just updated to OS x 10.10.3.
When I try to enter the Photo app, I get the message ״There is not enough disk space to migrate your library. It is estimated that you need at least 33GB of additional free space.״
I have a 256 GB SSD hard drive, Mostly occupied by images and videos that where in iPhoto app.
How can I delete images and/or videos to make room on my hard drive in order to use the Photos app and save it to iCloud.
Thank's,
Arik
MacBook Pro, OS X Yosemite (10.10.3)