Q: I'm currently using iPhoto 6 with Snow Leopard 10.6.8 on a Mac Mini (mid 2010). Can I directly update to use "Photos" on El Capitan?

Yes, you can. You'll need to run the iPhoto Library Upgrader afterwards.

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1 - you will need to download and run the iPhoto library upgrader - it is required for all versions older than iPhoto '08 (version 7.x.x)  --  Using the iPhoto Library Upgrader tool - Apple Support

2 - Photos is a new and totally different program with a learning curve - do not expect it to be the exact same as iPhoto - read the Photos help file and these articles for more information -

Notes on Migrating an iPhoto Library from iPhoto to Photos for Mac

Photos 1.5 vs iPhoto 9.6.1: Features and Capabilities

Details of how Photos handles the migration from iPhoto

How to Simulate Star Ratings in Photos

Photo Editing Extensions for Photos for Mac

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