The word Aham 'I' is often confused. When we say, Aham, it is just 'I' and not Ego. AhamkAra can be split into two words 'aham' and 'kara', aham means 'I' and kara means 'doer'. Hence the word ahamkAra verily means, 'I am doer'. This difference is not understood by most non-advaitins and hence they wrongly understand the Advaitic interpretation of mahAvAkya-s.
When I say, I am Brahman (aham BrahmAsmi - aham brahma-asmi), then some wrongly take it 'I' as Ego or 'I' as Jiva. For there there is an a priori (presumption) that I ma Jiva. Hence they understand that I, the Jiva, becomes Brahman. While Advaita says, I m not Jiva. Hence ask 'Who am I', the answer is 'I' am Brahman.
The word 'am' seems to create confusion. It makes us think that the word 'am' indicates 'to become' i.e. it denotes transformation. This would resemble to pariNAma vAda, in which milk turns into curd. While Advaita does not think in the same way. Advaita adopts vivarta vAda. Hence there is no transformation. Only wrong notion is removed.
I ≠ Jiva
I = Brahman
Advaita begins with dvaita and assumes or say presumes that 'I' is wrongly taken for granted as 'body' or 'Jiva'. Hence Advaita asks us to find this 'I'. Lets substitute 'am' in the above mahAvAkya with 'is'. The mahAvAkya becomes
'I' is Brahman
'I am Brahman' may seem to look like upadeshaka vAkya, but in reality it is a state of Self Realization. Put in other words, One realizes that 'I am Brahman'. For sake of understanding, to explain non-advaitins, we can say 'I is Brahman' as this will remove a priori and the wrong understanding of transformation.