...I didn't get a user manual with the (2nd-hand) Roku LT 2400X...
They actually just come with a Quick Start Guide. You can download one from here: http://www.roku.com/roku-products
. Just scroll down near the bottom of the page. One is listed under each device.
Roku 3, Roku 2, Roku 2 XD, Roku Stick (3600)
Apple TV (4th gen), TiVo, Chromecast
Roku Stick (3500), Roku 1, Roku 2 XS, Roku LT(2400), Roku XDS, Roku XD (2050)
Apple TV (2nd, 3rd gen), FireTV, FireTV Stick