A great resource for looking at and even editing EPW files is Elements. If you open your EPW file in Elements, you can click on the Dry Bulb Temperature column and then the Normalize by Month button above it. You can then change the Scaling Method to Scale by Minimum/Maximum and it while show you the Current Min and Current Max temperature for each month.

Open the EPW file in your favorite text editor - one that doesn't wrap lines after a certain column. I use Ultraedit. The top part of the file is header information. Copy the rows below that header information - starting at row 9 right to the bottom of the file. Copy that data into an Excel sheet, use Text to Columns with the delimiter set to comma. The 6th column is drybulb. Use an excel array formula to get the min and max for each month. On a second sheet, enter 1,2,3,4,.. for each month in a column. Then enter the min and max formulas beside the month number. In the example I just created: {=MIN(IF(Sheet1!$C$3:$C$8762=Sheet2!$B4,Sheet1!$H$3:$H$8762))}. For array formulas, type the formula then use Ctrl-Shift-Enter to specify an array formula. Note, in my example, the weather data starts in Row 3, Column B - adjust the formulas depending on where you paste the data from the EPW file.

I don't know why some of the items get bolded in my answer.

You can open EPW weather files in the DView application. Then simply go to the Statistics tab to view min/max for all the weather variables in the file. DView has a number of other visualization capabilities as well.