Sometimes, while downloading the ISO installation file, it may get corrupted on the way and becomes unfit for use. One possible solution that I know to deal with this problem is re-downloading the entire ISO file again which is very difficult for users with low bandwidth. Are there any alternative solutions which does not require the user to re-download the entire ISO file?
After you have downloaded the whole file, there's not so much you can do to fix it than a full re-download; except if you should find someone offering the file in (unencrypted, non-archived) parts, along with separate hash sums. Because otherwise you wouldn't even know in which part of the file the problem is, and therefore which part you still need again. I do not know of a program which does that for finished downloads.
So your best bet probably is to switch to a transmission tool like bittorrent, which does the splitting up into chunks internally, and which also checks hash sums for each of the chunks separately. For each part it will check if it was transferred correctly, and will re-download only that part if it was not.
In the end you will have the complete, correct file, without any manual intervention required.
You can use a download manager, such as FlareGet. FlareGet is a full featured, multi-threaded download manager and accelerator.
To install just click FlareGet
Or use a bit-torrent application to download the file.