It already is compressed (WorldEditor does that for you).
You will have to delete stuff from it to make it smaller. Vexorian's Optimizer is a good place to start as it will remove all WorldEdit only data from the map (warning, this will render the map unable to be opened in the editor so make a backup).
If the map is still too big, you will have to delete content. Large maps are mostly caused by imported assets such as skins or models. Deleting them or applying higher lossy compression (smaller filesize, worse quality) will reduce map size further.
More efficinetly structuring triggers (eg, avoiding procedural coupling) can also save space but we are talking kilobytes here for a lot of work.