1. Download "Root Browser"
2. Open "Root Browser" and Go to "root" folder
3. Inside root folder go to "data" folder
4. Inside data folder go to "data" folder [again]
5. Inside data folder go to "com.whatsapp" folder
5. Inside com.whatsapp folder go to "shared_prefs" folder
6. Finaly, You see all the files, search "com.whatsapp_preferences.xml" file and click open
7. Open file in "RB Text Editor"
8. Change value 16 to 500 and Save file and close
Done...!