Advisable to switch from 38 mm tires to 28 mm?
Two things to take into account.
Firstly, 28mm tires lower your bottom bracket by one centimeter when compared to 38mm tires. If your bicycle was designed with 38mm tires in mind, it probably has a quite large bottom bracket drop. With 28mm tires, you can touch the ground with pedals when cornering pedaling.
Secondly, from 38mm to 28mm is quite a large change. Are you certain that 28mm tires are what you want? They require far higher pressure and the ride is less smooth.
Considering that one of the best tires, Continental Grand Prix 5000, is available as 32mm width, I would pick this width in your case. (Don't do what I do; instead, do what I say -- I use the 28mm width of GP5000 but in my opinion 32mm may be even better for people not used to narrow high pressure tires.)
The rim width may also limit your tire options. A 28mm tire requires a rim at most 622 x 19C. If the rim is 21C, you should not use 28mm tires.