The Shower Room is a location in Yandere Simulator where students will be able to change their uniform in the future. It is located by the track as of the November 15th, 2015 Build. Before then it was to the right of the school entrance next to the gym.
Girls' Locker Room
When in the girls' locker room, Yandere-chan can change her clothes between the school uniform, the school gym uniform, the school swimsuit, or go nude and be covered by steam. Only two lockers are able to be opened at this time: Kokona's and Yandere-chan's. In the future students will also react to theft, especially of their clothing, but it is unknown so far what will happen next, or even to the player. 
In the future, the player may not be able to steal uniforms at all. Programming to do so would require changing a lot of students' AI and cause a lot of programming problems. YandereDev wants to avoid implementing this as of the March 2016 FAQ.
On Thursday at 7:15 AM, Kokona Haruka will go take a shower. She will leave her phone in her locker, which the player can steal.
Boys' Locker Room
There is a boys' locker room planned. It will be identical to the girls' locker room, but with different uniforms in the lockers. If the player walks into the room and is spotted by NPCs, her reputation will drop. The male NPCs will act differently based on their personas.  One of the reasons to go in there, as stated by YandereDev, would be to admire or steal something from Senpai.
This room contains a horizontal bath facing a painting of a mountain and three rows of stations for students to wash off. Of the August 20th, 2015 Build, when the protagonist is bloody, she must bathe in one of the stools closest to the girls' locker room. It will take around four seconds to wash off. She can then change into a new uniform. She must then dispose of the bloodied uniform at the incinerator or risk a Game Over due to incriminating evidence.
Since the school is rich, there will be a bathing room right next to this room. People will bathe in that room, and there will be the option to drown them, but there are no animations for this action at the moment. If in the future, if Yandere-chan drowns someone here, the body will have to be hidden.
- When School Atmosphere is high, the lockers will be unlocked because everyone is so well-behaved that no one is expected to steal. When School Atmosphere is low, students will lock their lockers so that no one can steal their fresh uniforms or belongings, thus increasing the game difficulty. This is not implemented yet. 
- YandereDev originally wanted to allow the player to frame people with uniforms. Yandere-chan would be able to leave her bloody clothes in someone else's locker, so when police investigate the lockers, they will think the rival committed the crime. However, he later said he changed his mind, as the police would find Yandere-chan's DNA on the clothing.
- As of the August 6th, 2015 Build, if Kokona Haruka sees a corpse while she is wet with blood, she runs to the shower room, cleans off the blood, and then flees the school.