If a motor fails prior to V1 you abort. If after V1 you accelerate to VR (rotate speed) and then climb at V2. (single engine climb speed) You continue to climb out at V2. If the engine fails after V2 you climb at the speed at which the engine failed above V2. Most flight directors command a speed somewhere between v2 and v2 + 20. Dont mess with the switches until you are at a safe altitude. Even an engine on fire still provides some thrust unless it has seized. Remember AVIATE,NAVIGATE and COMMUNICATE in that order.