select two vertices and click merge vertices.
if it doesn't work then the tolerance is too low
click the options box in the menu next to merge vertices and you'll see the tolerance thing.
personally i keep it low so when i merge two meshes together i can select all the verts and hit merge without all of them merging into one vertex.
you can change the merge tolerance as well in the mesh's history (provided you have history turned on)
that's a "Ch" pronounced as a "K"
Computer skills I should have:
Maya, XSI, Photoshop, AfterEffects, Motion, Illustrator, Flash, Swift3D