NetBeansのインストール先にある
etc/netbeans.confを編集する事と・・・

使用するJDKやNetBeansの起動オプションを
指定できるみたい・・・＾＾

To change the size only temporarily, set this start-up option in the commandline when launching the IDE. For a permanent change, put it into the netbeans.conf file which is found in the /etc directory of your NetBeans installation. Place the option as the last parameter into the netbeans_default_options variable: