Uprate when faster shutter speeds, smaller apertures in poor light, or extending the effective range of your flash is needed. Treat all fots on a roll of film the same way when you manipulate a film's speed rating. The amount you can change the ASA setting and still obtain acceptable results depends on the film speed. When your light meter fails to respond in dusk or night fots, replace the previously exposed film with a fresh roll of faster film. You may have to set a much higher ASA rating until it reads a workable shutter speed.
Uprated films require extra development or pushing.
Many processing labs offer this modified service. Avoid confusion by marking the film end with its revised ASA rating using a grease pencil when it is removed from the camera. To uprate film, turn the ASA setting control to a higher figure. If you double the film's stated ASA you are going to expose the film as if it were one stop faster. Three times normal speed equals a one and a half stop increase.