Repairing a damaged sliding shower door is not very easy, but with some little knowledge and skills, you can make it. Start by checking the door rails for a screwed guide rail. Remove the guide to allow you to lift off the shower door. Spin the rollers to see whether they are turning freely. If not, use a damp rag to clean and apply some spray lubricant. Return the shower door and test how it rolls. If the rollers are damaged, you will need to replace them with new ones.