recap the steps scattered around to here.
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1) SDG2042X: utility->system->system info, note down your Serial number and Software version. for example: 2.01.01.23R8
2) USB drive: format USB drive to FAT format, with MBR (master boot record) scheme. If you use GUID scheme, SDG2402X will not recognize it. It tells you it is removing media drive even you are inserting it in.
3) Firmware: goto
https://www.eevblog.com/forum/testgear/siglent-ads-firmware-file-format/msg1870091/#msg1870091, and download telnet_SDG2000X.zip, unzip to telnet_SDG2000X.ADS, put it on USB drive
4) SDG2042X: hook Ethernet cable, turn on SDG2042X, utility->interface->LAN Setup->DHCP on, write down IP address, for example: 192.168.1.20
5) SDG2042X: Insert USB Stick into front panel USB socket, put SDG2042X to utility->/System/Firmware Upgrade->USB0->find file: telnet_SDG2000X.ADS->Recall, updating starts and fails after a while. Yes, it fails. So your version is never changed.
6) SDG2042X: LEAVE POWER ON SDG
7) computer console: access to SDG2042X file. type: telnet <SDG IP address> <SPACE> 10101 <RETURN>, for example: telnet 192.168.1.20 10101
6) computer console, mount driver as writable. type: mount -o remount,rw ubi2_0 /usr/bin/siglent/firmdata0
7) computer console, make a backup. type: cp /usr/bin/siglent/firmdata0/NSP_system_info.xml /usr/bin/siglent/firmdata0/NSP_system_info.xml.orig

computer console, use "vi" editor to edit one file. type: vi /usr/bin/siglent/firmdata0/NSP_system_info.xml
9) computer console, move cursor down by typing "j", and right by "l" to the very first letter "<" of the line <license> and press "x" to delete anything between and including "<license>" and "</license>". After deletion, this line becomes only has "</system_information>". if anything goes wrong, you could exit "vi" editor by "esc" and ":", and "q!", and redo it again.
10) computer console, press the ESC key, then type: "wq" and <RETURN> to save the file
11) remote computer console, type: "sync"
12) SDG2042X: remove USB stick
13) SDG2042X: turn power OFF
14) SDG2042X: check utility->system->system info, and check product type and Serial Number