After the iphone4s chooses to erase all contents and settings, will the system version also be reduced to the factory version?

No, this is equivalent to formatting the memory area that individuals can allocate. Your custom settings, pictures, music, address book, SMS, etc. Will disappear, but your system version will not change.

After erasing all contents and settings, if the device can't start normally, the following methods can be used to solve it:

The computer needs to install iTunes.

Press and hold [power key] and home until it is turned off, and then release it.

Press the power button, and release the power button after starting the machine; Press home 15s or so. A screen connected to iTunes will appear.

Connect iphone to computer via usb.

Select [Restore].