Convert a field type

[sasis]

I would like to change a custom field from single select to multi select.It is not possible .How will i achive it

[Nic Brough -Adaptavist-]

You can't in the UI.

It's actually quite easy in the database though (caveats - NEVER run SQL on a Jira while it is running, and ALWAYS backup before you do this, and do a full reindex afterwards)

See https://confluence.atlassian.com/display/JIRA/Changing+Custom+Field+Types

Note that you can't go the other way, unless you're happy to lose data.