how to convert a custom field of check box to radio button in jira?

[M GOKARI]

how to convert a custom field of check box to radio button in jira?

[Nic Brough -Adaptavist-]

You don't.  There is no way to change the type of a custom field (and in this case you couldn't code for it either - the data the two types hold is not compatible - a check box can hold many selections, bit a radio button only one, you'd need to code to ask the users which values they wish to lose)

You will need to add a new radio button field, script or manually copy any content you want to keep from the old field into the new one, then you can delete the old field.