There is much hullaballoo in the UNP. The party leadership is critical and has implications for the choice of candidate and polices followed by the party during and after the elections. The UNP claims to stand for freedom and democracy. If so it cannot avoid a democratic method of selection to the Central Governing Committee and the key office bearers.
I think the best method is to hold a party convention at which all the members are represented and to elect the office bearers and the committee at such a convention as it happens in all organisations practicing democracy. But if the numbers are too large then either there can be a postal voting system or delegates may be selected by the Constituency Committees to attend a party convention at which the key office bearers are elected