The file uploader has a limit of 500 MB for either a single file, or a group of files in a single upload. However, some users will not be able to upload a file of that size due to limitations of their internet connection speeds, particularly the upload speed.
If you are having difficulty uploading large files and you get a timeout error before completion of the upload, the likely issue is with the upload speed available to you.
You can use the following free utility to measure the upload and download speeds you are getting via your internet connection here: http://www.speedtest.net (You should choose the New York server for the test, as it is the closest to the data center where your website server resides.)
If you would like us to help diagnose upload problems, please perform the above test and paste the link to the results in a Support Ticket. Please include the name and size of the file you are trying to upload.
Also, see this Support Blog post dealing with solutions for uploading video files which are too large.