If a spell must be maintained with concentration, that fact appears in its Duration entry, and the spell specifies how long you can concentrate on it. You can end concentration at any time (no action required).
End Concentration
ActionPHBp. 2032014SRD
Raw data
{
"srd": true,
"name": "End Concentration",
"page": 203,
"time": [
"Free"
],
"__prop": "action",
"source": "PHB",
"entries": [
"If a spell must be maintained with {@status concentration}, that fact appears in its Duration entry, and the spell specifies how long you can concentrate on it. You can end {@status concentration} at any time (no action required)."
],
"basicRules": true,
"reprintedAs": [
"End Concentration|XPHB"
]
}