First and foremost, consult the service center about the compatibility of technical equipment to Chinese phone and firmware that you want him to deliver. For example, if you want to put the original, it may not function due to differences in the technical features the original and Chinese phone. In this case, you will have to contact the service center for the firmware of the phone.
If everything is fine and the technical equipment of the phone will function normally with the original firmware. In order to install it manually, you will need to first sync your computer with your phone. If there is no bundled data cable and drivers, you will need to buy them separately, because flashing via bluetooth and infrared port impossible.
First, install the driver, then the software for the phone. Only after this connect phone to computer using usb wire. Remember that when flashing, you need to carefully follow the instructions in any case do not disconnect the phone until the firmware is completed.
In the service center to which you applied, can also be a Russian keyboard for your phone. Order it or buy if it is available. Also, if you think that the process of Russification of the phone is too complicated for you, you can contact them for the service of flashing the phone.