The Sims 4 has your sim wearing a uniform pertaining to whatever job they’re going to. In the Get to Work expansion, you can even follow your sim to work and this may be a bit of a hassle if your eyes need to keep looking at a hideous uniform. Unfortunately, there is no normal way to change your sim’s career clothes. EA has not, as of the time of this post’s writing, made it possible for this to be done easily.
However, there is this mod that will allow you to do it through the Create a Sim screen as though you were changing any outfit.
If you don’t want to install a mod, there is a sort of annoying fix. Make an outfit look like how you want your sim to dress at work. Once you get to work, change your sim into that outfit. Voila! Every time your sim leaves the lot or goes to work, you’ll need to remember to do this, though.