Modify FTP script

I would like to modify this FTP script below so that it does the following

1. Download any new files to the local directory.  (So the script needs to determine what it downloaded last time, so that it doesn't download it again, unless it it's easier to write the script so as to download everything it sees in the remote directory to the local directory and just overwrite any files which it sees, which is ok as well, in this scenario).

2. Does not delete the previous files from the remote directory.

@echo off
setlocal 

set password=xxxxxxxxxx
set /p password=<%~nx0:password
if not "%password%"=="" goto OK
set /p password=Enter password: 
echo %password%>%~nx0:password
:OK

set localdir=\\server1\main\
set remotedir=/out
set ftpserver=xxxxx.xxxxxxxxxxx.com
set username=xxxxxxxx

::del "%localdir%\*.*" /q

call :GetFtpFiles
call :ClearFTPFiles

exit /b

:GetFTPFiles
    (echo open %ftpserver%
    echo user %username% %password%
    echo bin
    echo cd %remotedir%
    echo lcd "%localdir%"
    echo mget *.*
    echo quit
    ) | ftp -n -i
    exit /b

:ClearfTPFiles
    (echo open %ftpserver%
    echo user %username% %password%
    echo cd %remotedir%
    (for /f "tokens=*" %%a in ('dir /b /a-d "%localdir%\*.*"') do @echo dele "%%~a")
    echo quit
    ) | ftp -n -i -d

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