Donate the PS4 to a Charity, Hospital, Care Home etc etc
Would be a nice gesture before you switch to the Xbox.
Reset it back to Factory Settings, remove all card details if you have any attached to your PSN Account. You don't want any nasty surprises a few months down the line because of a Rolling Subscription, as these are non Refundable items. So, go into Account settings, turn OFF the automatic billing request and delete them cards as mentioned earlier in this post.