From Biblical exegesis, the sages derive that when attending to the improvement of the seven flames, the priest does not adjust all seven lamps at once. Rather, he must divide this task into five and two: upon entering the Sanctuary, if he finds that the two "eastern lamps," that is, the two flames on the eastern side, are still burning - in that case, he attends to the other five, cleaning out the ashes and filling them with new oil and wicks. He places the refuse into the golden basket.
Even if he enters to find that the other five flames are still burning from the previous day, he extinguishes them and replaces their oil and wicks, and then rekindles them. This is the service known as "Improving the Five Flames." He leaves off the other two lamps for now, allowing them to burn as they were. After the blood of the daily sacrifice has been tossed on the altar (and according to other opinions, after the incense service has been offered) he will return to the Sanctuary to likewise attend to these two lamps in the same fashion.