Select Splashtop Whiteboard from the Windows Start menu to display the five-tab Splashtop Streamer dialog box, or use the icon in the Status Bar. Open the Security tab; then you can change the existing security code. A message will be displayed after a security code has been changed successfully. 
Your security code MUST be between 8 and 20 characters long; MUST contain both letters and numbers; and may optionally contain the following special characters:
/ ( ) $ & @ " . , ! ' [ ] { } # % ^ * _ | ~ < >
NOTE: In the Security tab illustrated above, the term "password" was changed to "security code" effective with Splashtop Streamer v1.5.5.0 and later versions.