Increase sga_max_size on Oracle 10g Windows

i would like to increase the max memory size of one Oracle 10g database installed on Windows.

The v$parameter shows

sga_max_size 452984832

and

sga_target 452984832

Note that the ISDEFAULT column for sga_max_size is TRUE and every other IS settings are FLASE

I have found a init.ora file in the adminMYINSTANCEscripts and i have changed both parameters and restarted the service with no success.

There is another init.ora file in srvmadmin folder but i don’t know if i can modify this one.

Where should i modify this parameter to have the memory increased ?

Thanks