Note that the beta version will work with your existing license. So, simply install RiverCAD Beta 4.0 in a different directory than version 3.5. Version 4.0 should see your license from 3.5 and run.
Please feel free to contact me directly if you have any questions or need any further information.
Sincerely,
Chris E. Maeder
Senior Technical Engineer
chris.maeder@bossintl.com