James,

There are many "sexy" ways to do it, but if you only have to do it
once or twice....

1) Calculate the mean and standard deviation
2) Calculate the upper and lower cutoff values
3) Sort the data
4) Manually delete those above/below the cutoff values

If this is something you will do on a regular basis, then it may be
worth pursing a more automated method.

HTH,
John