Nodes: To delete a node or
nodes, first select them, and then press the delete key, click the 
toolbar button, or choose Edit
→ Delete.
Alternately, you can just right-click
a node and choose Delete. This
will remove the nodes, and all links from other nodes going to them. Links
going from them to their child nodes will be disconnected
just before the deletion. These disconnected links will be selected
after the nodes are removed, so you can easily delete them as well by
just pressing the delete
key a second time.
If you wish to remove the nodes, but maintain the global relationship of the remaining nodes (i.e. the full joint probability distribution), you should absorb the nodes.
Links: To delete a link, click on it to select it,
and then press the delete
key or choose Edit →
Delete. To delete a series
of links, select them all and then press the delete key. When a link is deleted,
the conditional probabilities of the child node are collapsed to eliminate
their dependence on that parent, as if the parent took on its first state.
When a link is deleted the parent node is not affected in any way.