Japanese grammar has a rich subset of grammatical forms named 敬語 ("keigo", formal language or respect's language).
The rules allowing to transform a normal verb into a keigo verb are complex and I'm stuck with a difference I found here on a well-documented site.
For each verb it seems that there are TWO ways to create infinitive keigo forms :
- o either お + [い-stem] & に なる
- o either お + [い-stem] & なさる
By example : 変える (kaeru) becomes either お変えになる either お変えなさる.
I don't understand if the difference between these two forms is merely formal (like in French : je m'assois, je m'assieds) or if these two verbal forms are used in different linguistic contexts.