How to increase ignore above limit of a field in a elastic index?

[sabyasachi_mallick]

i have a field named "description " in a index in elastic.
"description":{"type":"string","norms":{"enabled":false},"fielddata":{"format":"disabled"},"fields":{"raw":{"type":"string","index":"not_analyzed","ignore_above":256}}}

but i want to change ignore_above field limit because i am getting longer strings in this field.
How can i update this field through put command or is there any other way to this?

[wenpos (Fanfan)]

You can update the ignore_above arg in this way
PUT my_index/_mapping/my_type
{
"properties": {
"my_field": {
"ignore_above": 20,
"type": "string",
"index":"not_analyzed"
}
}
}