@ TK, yes keep a copy is better. So for whom would want to try this. Here is a simple guide to upgrade SDS2104X Plus to 500 MHz.
1) Create a .txt file and input 'telnetd'
2) Save this file as 'siglent_device_startup.sh' . *** It must be this file name. And file format is .sh***
3) Copy file 'siglent_device_startup.sh' to the root directory of a USB drive.
4) Insert the USB drive to scope, and now turn on the power of scope. *** Must have the USB drive inserted before turn on the scope. And everytime you want to telnet to scope, you need to have the USB inserted before turn on it.***
5) After turn on scope with USB inserted, set scope LAN configuration as DHCP
6) Open a command window on PC, write 'telnet +IP address of your scope'
7) Now it requires user name and password.
User name: 'root'
Password: 'siglent_sds1000x_e'
After log in, write commands:
mount -o remount,rw,sync /usr/bin/siglent/firmdata0
rm /usr/bin/siglent/firmdata0/bandwidth.txt *** or as TK suggested, you can use another command to have a copy of this file just in case**