>can you copy a library from one location to another and overwrite the old one?
>
> This is the problem, I have an old libray on N:\dir1\prglig\... I have a modified libray with new classes on C:\dir1\prglib\...
>
> When I copy and paste the new library to n:\dir1\prglib\... and open it up the old libray is there not the new one. I don't know why this happens.
>
> I know I can do an add class or drag and drop classes, but can I just copy a library from one area to another and overwrite the old library and bring over all of the classes?

Yes, you can. Just restart VFP, because it might be, that the old version is still in the memory...