Can men or women, change their clothes completely or partially, without breaking their Wudu? Doesn't removing upper garments of women till bare or exposure of navel by men break Wudu?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Taking off clothes has no effect on one's ablution (whether a male or a female) even though one becomes naked, since uncovering the ‘Awrah (what is between navel and knee for man and the whole body except hands and face for a woman during the prayer) does not invalidate ablution. But if one touches the private parts (penis, vulva and anus) without some barrier, his ablution becomes null and void for the Hadeeth of Busrah bint Safwaan who reported that the Prophet said: “Whoever touches his penis (with his hand) cannot perform prayer until he performs ablution.” [Ahmad, Abu Daawood, At-Tirmithi and An-Nassa’i] Al-Albaani and Al-Arn’oot classified this Hadeeth as Saheeh (authentic).

On the authority of 'Amr Ibn Shu'ayb from his father from his grandfather that the Prophet said: “Whoever touches his sexual organ should perform ablution; and a woman who touches her sexual organ should perform ablution.” [Ahmad; Shaykh Shu'ayb Al-Arna’oot regards this Hadeeth as having a good chain of narrators.

For more benefit on the nullifiers of ablution, please refer to Fatwa 84093.

Allah knows best.