The simple thing to do is reload the OS on the phone with a clean load.
You can do a wipe on the phone and it will restore back to factory but you need to do a backup first.
The slow action may be too many Apps are loaded or the OS has corruption.
Go to the Blackberry site and download the free Blackberry Link software if you dont already have it. Then go to your carriers site or use Blackberry and down load the newest OS.
DO NOT put any OS on the device not intended for it.
This forum has information on upgrading and replacing OS on the Z10.
General Z10 Series Discussion - BlackBerry 10 - BlackBerry Forums Support Community
READ, READ READ before doing anything.