Negative exponents can be written as the inverse of a positive exponent. Use a simple example, x^-m = 1/x^m. No matter what the exponent is, it can be written as one over the positive exponent, like 2y^-9 = 2/y^9.
Write the negative exponent in the denominator of the fraction as the inverse of a positive exponent. This operation does not change the numerator of the fraction. For example; if the fraction is y^2/x^-3, write it as y^2/(1/x^3). Keep the denominator in parentheses to avoid confusing it with elements of the numerator.
Complete the division of the fraction. Simplifying a fraction in the denominator of a fraction can be done by writing the fraction as the multiplication of the numerator and the inverse of the denominator. To use the example in Step 2, write y^2/(1/x^3) as y^2 * x^3/1. The 1 in the second part of the operation can be removed, since it is just the identity; the result is y^2 * x^3.
These imply a shortcut to removing the negative exponent. It is possible to simply move the negative exponent from the denominator to the numerator and change the sign. For example; z^4/x^-2 simply becomes z^4 * x^2. By using this shortcut, you perform the same operations as in the previous steps, just without writing out each step.