You will need.
1.Soldering iron/soldering iron stand
1.hubsan x4 motor
Step 1: Getting ready
Unscrew back cover and heat up your soldering iron
Step 2: Motor detachment
Take your Hubsan x4 back cover off. Heat your soldering iron and, quickly tap the solder pad.
Step 3: Motor extraction
Take a screw driver and lift at the motor wires. Then grab some plyers and twist at the motor, to remove it.
Step 4: Motor attachment
Take your new motor, slide it in, and lay it on the soldering pad.(make sure you match up the right wires with the right solder pad, etc. red is positive blue is negative, white is positive and black is negative.) Then solder it, but your back cover on and your good to go! (Tug a little after soldering to insure durability) Good Luck