https://confluence.atlassian.com/display/JIRA/Increasing+JIRA+Memory

The above page tells user's to edit senv.sh or setenv.bat file inside the <JIRA Installation Directory>. Wherever possible, we should stop recommending people edit files within that directory, if there is an alternative. Each edit you make within that directory is an edit you have to re-apply each time you upgrade.

A better alternative is to get the admin to set an environment variable before starting JIRA. This environment variable is called JAVA_OPTS and the min and max settings can be specified with the -Xms and -Xmx parameters. For example, in Linux:

export JAVA_OPTS="-Xms768m -Xmx1g"

Advantage of using an env var is that it eases upgrade, at the expense of having to somehow set an environment variable before JIRA starts. Setting pre-start environment variables is something we have not documented well yet. (Although this page does mention it.)

Advantage of telling people to edit setenv.sh is that it makes it easier to document what to do, at the expense of making upgrades harder or more brittle.