By performing a factory reset will delete and wipe all of your personal data, so we highly recommended to backup your important data and take the SD Card out from phone before performing factory reset.
Samsung Galaxy Mini S5570 Hard Reset Procedures :
1. Power off phone
2. Press and hold Menu Button ( middle ) + power on for at least 10 seconds
3. Android System Recovery Mode Appear
4. There are 4 options
reboot system now
wipe data/factory reset
wipe cache partition
5. Move the options to " Wipe data / factory reset " using volume down ( - ) button and menu button to confirm, because the touchscreen doesn't work in reovery mode
6. After the process done, phone will reboot.