To change the password for your file manager first login using the default credentails provided on the welcome page.
Once Logged in you can generate a new password hash here - Admin > Help > Generate new password hash
Once a password hash is created, copy it to your clipboard and go back to the root directory.
Go in to the folder uploadfiles and click on the finyfilemanager.php file and click Edit.
Within the Single Quote you will replace the exsisting password hash with the one you created as seen within the image.
Be sure to do this for both admin and user.
In the case that you dont need the file manager you can remove it to increase security.
To remove the file manager simply login to the filemanager and locate the folder named "uploadfiles".
Click the trashcan icon on this folder and remove it.