I am new to Final Cut Pro and I have made the mistake of copying my imported media to the library (dublicating it) now my library is too big 1.84GB so how do I delete the raw files that I have copied into the library without stuffing up my project

Have you already consolidated to move the clips out of the library? That would be the safest first step. You can then use the relink function to relink files to the original media wherever it’s stored. Once it’s correctly relinked the way you want it, you can throw away the media that was moved out of the library.

Yes, you should be able to relink your library to the folder on the external drive containing your original files. Do the consolidation first to move all the files out of your library into a new folder, then do the relink to the external drive. You should end up with a svelte library pointing to your external drive for footage.

Relink clips to media files in Final Cut Pro - Apple Support

There are two ways to do this. The safest is to let the application do it for you. Select the library in the application and in the inspector click the Modify button next to locations. Make a folder to store your media wherever you want, like a fast SSD. In FCP assign the folder as the storage location for the media, then click the Consolidate button. The media will be moved to the San original media folder in the assigned location and replaced inside the library with symlinks.

The library actually isn’t all that big.

Great!