Flashing ROM means re-installing the operation system of your Android. When it comes to flashing ROM, you may wonder whether it is safe to flash a ROM on your Android phone. Well, to be frank, there are risks and disavantage to flash ROM: some Android phones will fail to reboot, get crashed, lose data after failing to flash a ROM. To avoid these errors, there are some tips and tricks for you to follow and reduce the risk of flashing ROM. Let us specify them one by one.
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Top 5 Tips to Reduce the Risk of Flashing ROM
1. Always Make A Backup First
Note that backup is the most important preparation before flashing a ROM . Remember to back up your important files on your Android phone, such as contacts, SMS, photos, etc.

2. Download A Suitable ROM
You need to download a ROM according to the model number of your device. It is important that you have downloaded a suitable ROM for your device. If you flash a wrong ROM for your Android device, for example, flashing the ROM for Samsung SM-G935F on a Samsung SM-G9350, the Samsung S7 Edge might be bricked. You can download a ROM from XDA forum or others.
If you need to flash a official ROM, you can download the suitable ROM for your device from its manufacturer's website.
For Samsung users, visit: http://www.samsung.com/us/support/
For HTC users, visit: http://www.htc.com/us/support/
For LG users, visit: http://www.lg.com/us/support
For Sony user, visit: http://support.sonymobile.com/us/
For Google Nexus, visit: https://support.google.com/nexus/
3. Follow the Flashing Steps Strictly
Operations of flashing a ROM vary with different brands of Android phones. You should read the instruction carefully and follow every step strickly during flashing a ROM on your device. For example, since many guides point out that it is important to have enough battery for the Android phone to flash a ROM, you should follow the guide and make sure that your Android phone battery is no less than 50% power left.

4. Ask For Help
If you still have questions about flashing a ROM after reading online tutorials, get help from the experienced users before rushing into anything. Maybe you have some tech-savvy friends who have flashed ROM on their Android devices, ask them for help or let them flash the ROM for you. Or you can post a thread on Android forums to get help from the professionals.
ROM versions are designed on the basis of the original editions. It will change the images, ringtones, menu but not the kernel partition. So it is of little risk once you have previously backed up your data and follow the instruction faithfully.
But you should aware of the disavantages of flashing a ROM. The warranty of a flashed-ROM Android phone will be in vain and you phone will fail to have the free maintenance service. So think before you act.