Q: How do i uninstall iPhoto?

Are you sure, that each and every photo imported correctly to Photos and you will not need iPhoto to repeat the migration to Photos? If you should  later discover a corruption of the Photos Library that can only be fixed in iPhoto you may need to revert to iPhoto. Also, Photos is missing quite a few features you had in iPhoto, compare:   Photos vs iPhoto:  Features and Capabilities

I recoomend to keep a backup of your iPhoto Library and the iPhoto application on an external drive, just in case.

To uninstall iPhoto drag the iPhoto application to the Trash, that will just save 1.7 GB, you don't gain much space.

You can also trash the iPhoto Library from the Pictures folder, but that will not free much space, since the photos are shared with the new Photos Library, both libraries are using the same image files, see:   Photos saves disk space by sharing images with your iPhoto or Aperture libraries - Apple Support

When i upgraded to Yosemite, all my iPhoto pics automatically migrated to the new Photos Library. I checked and made sure all photos migrated.

You can only be sure, if you opened each and every photo in Edit mode. Then you will know, that the originals are correctly linked to the thumbnails and can be read.

How to - drag it to the trash and empty the trash

BUT

That is a really bad idea and has no advantage as doing so will make getting it back difficult to impossible if you want or need it and will save almost nothing

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