Please find the below given link to download latest standalone build of FTP Attachments®:

http://downloads.ftpattachments.com/builds/standalone.sforce.zip

Below are the steps to upgrade your application:

1) Rename existing sforce folder which you had originally installed as sforce-old.

2) Download the latest build from http://downloads.ftpattachments.com/builds/standalone.sforce.zip

3) Now copy License.dat file from sforce-old/App_Data to sforce/App_Data folder.

4) Make sure the Account under which your ASP .NET worker process is running, has full rights on sforce/App_Data folder.

5) Now all users will be using the new builds automatically.

6) We recommend backing up both old and new folder in separate server or backup space.

7) Once you are satisfied with the newer version (after couple of weeks) you can remove the sforce-old folder.