Replace the text
PARAM NAME = DATAURL1 VALUE = "http://www.mycomputer/mydirectory/eims1.jdx"
PARAM NAME = DATAURL2 VALUE = "http://www.mycomputer/mydirectory/eims2.jdx"
PARAM NAME = DATAURL3 VALUE = "http://www.mycomuter/mydirectory/eims1.dxy"
PARAM NAME = DATAURL4 VALUE = "http://www.mycomuter/mydirectory/eims2.dxy"
that is now written in the applet definition in this file. The new text must indicate the full address of the directory containing the JDX files rather than the arbitrary "www.mycomputer/mydirectory" that is presently written there.
If you are viewing this html file from within a browser, you can see the code that calls the DXYPlot applet by clicking on the view panel in the menu and choosing "document source" (Netscape) or just "Source" (Internet Explorer). You can edit the html source code with a simple text editor or by using the HTML editor that comes with your browser.