Apply the exponent rules. First combine the numerator using the product rule $a^m \cdot a^n = a^{m+n}$:

$a^2 \cdot a^4 = a^{2+4} = a^6$

Then divide using the quotient rule $\frac{a^m}{a^n} = a^{m-n}$:

$\frac{a^6}{a^6} = a^{6-6} = a^0 = 1$