In MESH you can change the location of any node of your mesh. In this case all adjacent elements (edges) will be also transformed right after the displaced node.
To displace a node:
From the Modification menu choose the Move node item or click "Move Node" button in the toolbar.
The following dialog box shall appear:
The initial mesh
The node has been moved, transforming all adjacent edges
See Also a sample TUI Script of a Moving Nodes operation.