how to convert user app to system app in android phone

AS you know that ......in android phone there are many types of.... system apps which you can't delete from your phone.......like... settings, gallery, camera, playstore, browser,

now i show you how to canvert user  apps to system apps   ....... and how to  canvert system  apps to user app apps

steps 

1. have a root android phone.
2. install (link to sd) app from playstore.
3. open it
4. click and hold on any user apps which you want to convert system apps
5. them select choose (convert to system app) option
6. after process phone want to reboot it
7 reboot your phone
8 after reboot check your app it will convert in to system app which you can,t delete

Advantage

if you want to formet your android phone but don't want to lose your data apps like whats app  and more apps ..
convert them to system apps and do formet to your phone ..
whats app and more importent apps do not be del from your phone like more system apps ..