How Can I upload files on blogspot ?

You can only upload image files to blogspot (blogger). For other types of file you must find your own hosting.

There is a limit of 300MB on the images you are uploading to a BlogSpot blog.

So you need to use free services like
windows live sky drive
Adrive.com
and i will soon post the list of websites which provide this kind of free services for uploading of files.
If you need to know the names very soon let me know.