Please get familiar with Telnet/Busybox/Linux (in reverse order), first.
It is easy to cause damage through a simply typo - remember that you are logged in as root!
The command you need is "mv", but you may need to use options like "-r" for recursive. But: you cannot just copy the relevant folders of the Siglent software, as the USB disk is mounted inside the application folder and hence it would be a catch-22.
Get the document everyon is talking about in the last few pages of this thread and read it carefully: it explaines everything in detail, even for people less experienced.
Cheers,
Vitor