yes, it’s safe, you will only lose configuration.

1. make backup of current firmware using avrdude
2. before update, connect to serial using telnet and type $$
3. save all results!
4. download latest firmware update https://github.com/gnea/grbl/releases
5. update
6. connect and type again $$
7. check configuration before update and ater
8. fix conifiguration, using syntax ”$10=100” etc.
9. done