You must remove the film rollers to properly clean them.
Dirty film rollers are the biggest cause for picture problems.
If you cannot figure out how to get the rollers out of the camera, please refer to the manual which has sketches and step-by-step instructions (instructions are also below). You should remove, check, and clean (if necessary) the film rollers after each pack of film. This is the most important step to obtaining good usable pictures. As you clean the rollers, turn them to make sure all surfaces are clean. If the rollers have not been cleaned for a long time, soak them in warm water and use a tooth brush to scrub them clean. (Do not disassemble the film roller assembly unless you know exactly how they go back together.) Also, clean inside the film back door, and the film exit slot.