Once you have the latest version of Photoshop CC, make sure you create a path to use this feature otherwise the option will be inactive in the menu. I found this helpful:
You need to create your path first (using the pen tool or any of the
shape tools), then choose Filter > Render > Flames. (Note: you need
to have a pixel layer targeted in the Layers panel as a landing place
for the flame to be created, not a Shape, Type, or Smart Object layer.
You can however convert type to paths or use the Type Mask tool to
render paths for letter forms).
As you can see from the dialog below, there are a large number of
options that can be customized in a number of ways. The six different
Flame Types are:
• One Flame Along Path: A single flame will be rendered on each path.
• Multiple Flames Along Path: More than one flame will be rendered on
each path. The flames will follow the direction of the path.
• Multiple Flames One Direction: Multiple Flames will be rendered on
each path. All of the flames will point in the same direction.
• Multiple Flames Path Directed: Multiple Flames will be rendered on
each path. Each Flame will point according to the path angle.
• Multiple Flames Various Angle: Multiple Flames will be rendered on a
path. Each Flame will point randomly. You can control the angle
variation by changing the “angle” parameter.
• Candle Light: One candle light will be rendered on a path.
Source: Flame Generation comes to Photoshop CC!