If you have an ethernet port somewhere in your wall, that is how to do it. Connect your personal router to that port with an ethernet cable, then connect to your router's wifi instead of the complex's wifi.
While, if you do have an ethernet port somewhere in the apartment that will work and what I explained will definitely enhance the amount of bars you get to the wifi it will not guarantee that when the complex's main router screws up you're still going to be able to connect.
The answer I suggest you consider is getting your own internet. It will be waaaaaayyyyyyy more reliable than the complex's connection for several reasons, the main one being what you described and another reason being that if there are a lot of people connecting to it and it's a DSL connection it will get bogged down and be slow. You won't have these issues if you call an internet provider and have your own internet connection activated. If you have cable television channels, that's not usually provided by an apartment complex included in the lease agreement, getting your own connection is as simple as calling the television company and telling them you want internet included in your account's package.