if you are using editable poly mode (this is what i work in), then to weld, you can either select the two verts, right click, weld selected. or you can right click, target weld, click the first vert and then the one you want it welded to.
to remover unused verts, on the side panel, select vertex edit mode (or hit key "1") scroll down a little, and hit "remove isolated verticies".