Increase sga_max_size on Oracle 10g Windows
Normally Oracle no longer uses the init.ora file anymore. It uses the spfileSID.ora in the $ORACLE_HOME/dbs directory. This is a binary file. Tio change the parameter(s) you should use:

alter system set sga_max_size=XXXM scope=spfile;


Now restart the database and the SGA_MAX_SIZE should be set at XXXM. Now you can alter the SGA_TARGET:

alter system set sga_target=XXXM scope=both;