Hi Saikiran
Currently when using Ambari you cannot make changes to the hive-env.sh. If you need to increase the hive heap size you can from within Ambari under services->HDFS->General change the Hadoop maximum Java heap size to the size that you want Hive to use. You will then need to restart HDFS and HIVE. You can then verify the heap size by running the ps -ef | grep hive and you will see something like the following with -Xmx<heap size>m
hive 13401 1 9 08:04 ? 00:00:09 /usr/jdk64/jdk1.7.0_45/bin/java -Xmx512m
Starting in Ambari 1.7 you will be able to edit the *-env.sh files
HTH
Donnie