It is always recommended to retract or pull back the foreskin during shower time to maintain cleanliness of the glans or the "head" of the penis.
If you are unable to retract the foreskin due to discomfort, I would advise a trip down to the urologist to get it checked out.
Depending on how tight the foreskin is, I would sometimes offer topical steroids and gradual retraction everyday. If that does not solve the problem, circumcision would be something to consider.
The most important thing to note is while you can be enthusiastically retracting the foreskin, always remember to return the foreskin to the initial position where it is still covering the glans of the penis.
Man with tight foreskin who do not return the foreskin can end up with paraphimosis where the foreskin is stuck behind the glans of the penis causing pain and swelling necessitating the need to make a trip down to the emergency room to see the urologist on call.