Advanced -> Modify Tileset...
Located at the pulldown menues at the top of the screen.
Using a third party modified editor like the on JNGP has you may be able to load more texture slots worth of terrain into your map. However WC3 still does have a hard coded limit so be warned that you may not get as many as you wanted loaded into a map.
Also I do advise thinking about your posts carefully before posting. Yours seems to be a bit offtopic in some areas and does not get straight to the point.