Does it break my wudu if:
I use a towel and change my clothes?
I become completely naked and then wear the fresh clothes?
No, Changing the clothes with or without towel does not break the wudu. As stated in a similar topic on this link
Many amongest the public believe that unveiling one's own knees or Sitr (private part of body below navel up to knees) or looking at one's own or someone else's knees or Sitr nullifies Wudu; this is a wrong concept. However, to keep the Sitr covered is one of the manners of Wudu; in fact the Sitr should be covered immediately after Istinja (excretion washing). To unveil the Sitr unnecessarily is prohibited and to unveil it before others is Haram. (Bahar-e-Shariat, pp. 309, vol. 1)
Hence, from above statement it is clear that changing clothes doesn't break/nullifies Wudu.