I am working on a osCommercre project, in which there pages for uploading the reference files, we have given functionality to upload the file upto 100 MB size, Now the client Complains me that customers are complaining for the late upload of files, what should i do to increase the upload speed?
You can probably do small optimization in your code, however, you can do nothing about files as large as 100 MB size. Uploading process will be slower with files this size :( Same as the case with sites such as gmail, yahoo, etc.
What upload speed do they have? In my experience the user usually complains even when they have maxed out there own available upload speed from their ISP. Ask them what advertised speed they do have, and then check if they have maxed out that speed (remember that 1 MB = 8 Mbit).
If they have a lot of bandwidth, check with the hosting provider/your sysadmin.
Did you investigate what the real bottleneck is? This is all about upload speed, and the most obvious cause is that the clients have not enough bandwidth. Even if they use a fast ADSL, they could still have low upload speed (the "A" in ADSL stands for "Asymmetric", i.e. fast download, but slow upload).
For example, with a typical (for Europe) upload speed of 512kb/s, to upload a 100MB file it will take at least 26 minutes, assuming full speed (which is not the usual case)...