FTP Download Sizes/Limit

I am using the ftp library to access a FTP folder that will Hold txt files fill with XML data. I am trying to download those txt Files to parse the XML to update my website database.

The Final process will be something like this.
      1.The FTP folder Has the XML data i need.
      2.Download the file to local server, and delete the original on the FTP
      3.Parse XML data, to generate SQL query
      4.RUN SQL query on Web Site Database
      5.After Query is completed, delete the file from local server.


The problem is before i can get to step 3, Step 2 fails when the FTP folder has larger files. Not all files are downloaded, using the below example only FileOne is download. Instead of the php scriptending, i get a 500 Internal error so i am assuming the browser or something timed out.

ex.  FTP folder
     -----FileOne.txt  176,301,908
     -----FileTwo.txt     2,020,541
     -----Filethree.txt  10,050,654
 

Any Info on how to accomplish the tasks im trying to do, would be very helpful.