No need to get a professional to restring the uke. While part of a setup often entails putting strings that are more suitable for the uke on it that's not where the real skill is needed - the skilled part of the setup is adjusting the height of nut slots, making sure frets are level, rounded, and polished, and adjusting the height of the bridge saddle.
Depending on what kind of strings are on the uke, your playing style, and how much you play, strings can last anywhere from a few weeks to several months or more. Generally speaking fluorocarbon strings (Worth clear and brown, Martin 600, and several other brands) are very tough and stable and will last a long time (several times longer than simple nylon strings for me). Aquila strings have a covering that will wear fairly quickly - I use my nails a lot and I can pretty much destroy a set of those in three weeks or so on a uke I play a lot.
John