Article : OpenVPN_change_Password

Remove the Password :
openssl rsa -in client.key -out client2.key

It will prompt you for the current password, and write the decrypted key to client2.key

Add or change the password:
openssl rsa -in client.key -out client2.key -des3

It will prompt you for the current password (if any), then for the new password, and then write the encrypted key to client2.key