If you use a Mac or have more than 4 files to upload it would be best to upload them as a single compressed file by following these instructions.
Take all the files for the job and put them in a single folder whose name is your company name.
Compress the folder as a .zip file using Winzip or PK Zip if it’s a Windows platform file. Use Stuffit on the Macintosh platform and BinHex encode the file so that your file will retain its resource fork and arrive happily with its icons intact.
If your files are extremely large you may want to compress them into several archives such as companyname-1.zip, companyname-2.zip, etc. Sometimes it is easier to successfully upload 3 25MB files than it is to upload a single 75MB file.
You can download the programs from the links below.