upgrading firmware on stack with two GSM7328FS

Hello Fellows!!!

I have a stack switch with two switches GSM7328FS.
I want to upgrade the firmware in both switches to the latest version 8.0.3.34.
I did the following :

1-I disconected the second switch (slave) from the stack for upgrading the firmware.
2-I reset the switch to its default configuration following the procedure shown in the documentation

After that, the switch continue showing in its display the number 2 as if it was connected to the stack and I can´t connect to the switch.

¿Which is the problem?
¿What did I wrong so the switch never go to its original state (default configuration)?
¿Which is the best way to upgrade this stack?

Thanks in advance, Carlos.