You can launch the Update Assembly References tool either from an Progress Developer Studio for OpenEdge menu or from a command prompt.

From Progress Developer Studio for OpenEdge

From within Progress Developer Studio for OpenEdge, select OpenEdge > Migration > Update Assembly References.

From a command prompt

Open a Proenv command shell and enter updasmref.exe at the prompt. You can optionally include an argument specifying the assemblies.xml and toolbox.xml files to be updated as follows: 

updasmref -files <file_paths>
Note: file_paths is a comma separated list of files.