Air is not flowing freely through the evaporator coils. brush the dirt from between the aluminum fins. if they are all bent then straighten them. If that does not work then just replace it. because of cost efficiency. because you are hot. and you need it now and not later.
Four years is about average for a window unit. If it is freezing then it is not the refrigerant. Probably it needs a good cleaning...including the filter. Window units are sometimes not easy to clean. One service call would probably cost as much as a small new unit. If you are a handy person you could install a new unit... if you expect to have someone install it for you then it is sort of a toss up cost wise between having it serviced or replaced. I would replace it.
Yes you can have it recharged
