To add a little more detail, the primary differences are:
A bunch of things got renamed on the advice of lawyers or to make things clearer. e.gs Magic Missile ->Force Barrage, Spell Level -> Spell Rank
Alignment got removed and replaced with Sanctification (holy or unholy), Anathema and Edicts
Wizard Schools got reworked for lawyer reasons
Witch Class got some reworking
Lots of ancestries, monsters, and items got renamed, sometimes with small changes, for lawyer reasons. E.g Dragons are no longer color coded, but more based on different mythologies and archetypes.
To add a little more detail, the primary differences are:
Edit: Paizo's overview of the changes is available at https://downloads.paizo.com/RemasterCorePreview.pdf