$\displaystyle \text{Find } y' (1) \text{if } y(x) = \frac{1}{\sqrt x}$

Hi, I need help completing the question above. Here is what I have so far:

$\displaystyle = \frac{y(1+h) - y(1)}{h}$

$\displaystyle = (\frac{1}{\sqrt (1+h)} - \frac{1}{\sqrt 1}) * \frac{1}{h}$

Am I correct so far? What do I do next? (and why do I do what I do next?)