how do i force itunes to re-scan my library for changes i have made to metadata and artwork ?

I have a large music library and until 3 months a go I thought it would be too hard to organise it. Thankfully there are some good programs that help with this process and I have made many changes to my files/itunes library.

One program is supported by iTunes but it still leaves me with the old genre catagories in numbers which iTunes seems to deal with automatically ? Pity it didn't change them automatically ? Anyway I'm still not sure what to do with them as I might have a catch 22 situation ? Please read on !

This program also doesn't make cover art changes more specific......for example less than 250kb + <1000x1000 pixels for iphone and no option for embedding & folder.jpg for my Sonos system.

So I needed to use other programs.....Right so now I'm getting to the point!

Now all my changes have been made, it is not so clear what is actually changed ? Some of it might only changed the info associated with the files according to my iTunes Library Database or some of it might actually of modified the actual metadata of the files on my hard drive.

What I want is for the metadata to be correct at the source AND then of course I want iTunes to have the same information too.

I think that whatever way I have been doing it HAS actually modified the files at source but I can't be sure.

What I do know is that the changes I have been making for the last week are not shown in iTunes until I play the track/album.

I have tried suggestions from forums to force a re-scan and none have worked.

I have tried add to library an album already in the album which is supposed to not make duplicates and just update the changes, this didn't work.

I have tried get info on my entire collection and change nothing then clicking OK but that didn't work.

I have tried get info and entering a comment field on just an album to test and it didn't work!

I would really like to know if there is a way to update the library & I would love to know if and how to get all my info in iTunes to be permanently reflected at the source.

Thanks in advance and thanks for listening ;-)