Reprogramming FE 375:

This link will take you to the page you need, to get started:

http://consumer.schlage.com/Service-Support/Pages/InstructionandManuals.aspx

Then scroll down to this heading on that page:
Electronic Security-Keypad Entry Flex-Lock...
There's a wealth of info under that heading. You will be able to see a PDF file of the original print instructions, as well as a video of how to install the lock. This is useful because there should be a sticker to be found on the backside of the keypad, with the code number that you need to reprogram the lock.
Of particular interest to answer your question, this link will take you to the PDF file for the installation and programming of your lock. You will want to use the information under the Programming section:

http://consumer.schlage.com/Project%20Documents/P515-859.pdf

You will need Adobe Reader installed on your computer in order to view PDF files, so if it doesn't display for you, get and install Adobe Reader from here:
http://get.adobe.com/reader/

This installation video (fourth item down) will be useful to allow you to disassemble it and view the sticker. This is also a great time to change the 9-volt battery!
The ninth item under that same header is a video which walks you through how to reprogram the keypad to your new code, using that program code that you found on the backside of the keypad.

Good luck!