Your UPVC windows should last between 15-20 years before you start to think about replacing them.  If you are unsure about the quality of your frames, your installer will be able to inspect them and give you an appraisal.

Unlike timber frames which can rot over time, UPVC frames will remain sturdy throughout their lifespan.  The nature of the UPVC material means that it will last well, however there are other areas which also need to be considered including the locking system which may become damaged over time, and the double-glazing panels.  Regular servicing and lubrication of the locking system as well as keeping the fastenings clean will help to prolong the life.

If you start to see condensation forming inside your glazing panels, then it is possible that they have "blown" and the seal between the panes has become damaged.  If this is the case, then you will need to consider replacement.  While it is possible to only replace the glass panel from the window, it is often easier to replace the whole unit at the same time.

An advantage of UPVC window frames is that they are recyclable many times, which means that updating to a new window frame has minimal impact on the environment.