You will need to iterate through all of the know theoretical distributions to find the correct distribution to use. In Excel for Windows, there is EasyFit. There is also ExpertFit for Windows.

If you are comfortable with R, you can find the minimum log-likelihood function of each distribution.

<http://stackoverflow.com/questions/4290081/fitting-data-to-distributions>

The Kolmogorov-Smirnov, Anderson-Darling, Chi-Squared Goodness-of-Fit Tests should be able to help you.

http://www.itl.nist.gov/div898/handbook/eda/section3/eda35g.htm

Let me know if you need anything else.