Pull the power plug while it is switched on.
When the PS4 reboots, the downloads would have stopped and you can resume them individually one by one if that is what you prefer.
I except no responsibility if you pull out the plug while PS4 is powered on.
There is no proper way of pausing them at the moment, it sucks. But usually i will start downloads before bedtime put it in standby mode and let it do its thing during the night.
Later this year they will add support for pausing/resume downloads
Very easy work around for this, go to settings and then to network. Un-tick the box that says connect to the internet.
Wait a few moments and all the downloads will fail. Turn the setting back on again and go play online or start them again the way you want, The downloads will resume and not restart with this method