Property sharing

Dear Sir,

We r 2 brothers in the family, we r from a middle class family.

My elder brother was given 18 cents of land and one lakh in cash as part  of property sharing  few yrs ago as part of propery sharaing and we agreed to give little more after the death of my mother. We bought a 1 Acre of land with 5 lakhs about 15 yrs ago. Now the land value has gone up, he wants increased share of  property( 1 Acre property in my name)

What will be the legal advice.......

Thanks & Regards,

Deric