Over the course of time the Sun's spectral analysis will gave a stronger Helium and weaker Hydrogen reading. Explain why this will happen.

mattbrady's answer is correct.

The Sun is a yellow main-sequence star near the middle of its life, so it is currently in the process of converting hydrogen into helium by fusion. In several billion years it will run out of hydrogen; when that happens, it will expand dramatically into a red giant (most likely engulfing all the inner planets, including Earth), and begin to fuse helium into carbon.

Well before that, however, the Sun will partially deplete its hydrogen reserves. If astronomers took precise enough spectral measurements over a long enough period of time (unlikely, but impossible---if we can measure gravity waves, we might just be able to do this), they would observe very subtle changes in which the quantity of hydrogen detected slightly decreased and the quantity of helium detected slightly increased. Within a human lifetime or even the lifetime of a civilization, this effect would be very small---about one one-millionth of the Sun's total hydrogen has been used up from the time when humans invented agriculture to today. But we might just be able to pick it up if our instruments were sensitive enough.