Why would you want to change file size? You would have to use some type of file converter to change the format. For exanple you would need an audio file converter to convert a wav file to an MP3 file or a WMA file. MP3 files take up about 1/5 of the space and WMA files are about half of the size of an MP3.
How do you change a file size?
You cant exactly change a files size. Unless its a movie file, then you have to cut it down. Same with a music file. For a picture: make it smaller. But if its a program file, you might have to zip it in pieces using winzip. Thats the only way.
How do you change a file size?
By changing the content of the file. Though that depends on exactly what you need to do and what type of file it is.
Open it and compress it.
What type of file is it?
If a photo, you can do it using Widows Picture Manager by saving in different format.