Which of the fractions given below is not equal to $\frac{13}{19}$?

Let's simplify each option to check if it equals $\frac{13}{19}$:
* Option A: $\frac{39}{57}=\frac{13\times 3}{19\times 3}=\frac{13}{19}$ (Equal)
* Option B: $\frac{91}{133}=\frac{13\times 7}{19\times 7}=\frac{13}{19}$ (Equal)
* Option C: Let's check $\frac{195}{247}$.
$195÷13=15$. If we multiply the denominator by 15: $19\times 15=285\ne 247$.
Actually, $247÷19=13$, so $\frac{195}{247}=\frac{15\times 13}{13\times 19}=\frac{15}{19}\ne \frac{13}{19}$. (Not Equal)
* Option D: $\frac{208}{304}=\frac{13\times 16}{19\times 16}=\frac{13}{19}$ (Equal)

Therefore, option C is not equal to $\frac{13}{19}$.