Currently my clan leaders account has been locked and he is having a problem to reclaim it and alot of problems has popped up because of it, so i was wondering if there is a way to change clan leaders till he can reclaim his account.
There's only 3 ways that the leader of a clan can be changed. The clan leader position can be changed to another player by the current leader either demoting himself/herself, by leaving the clan, or by Jagex removing an inactive clan leader at the request of a current deputy.
The first two obviously require the clan leader to perform the change, but the inactive clan leader removal requires 12 months of inactivity (not logging in at all), a permanent ban, or disabled hardcore ironman (when death results in not being able to log in) of a current clan leader in order to qualify for a change of clan leadership.
Unfortunately, your clan would not fall into any of these criteria, so you wouldn't be able to make this change in your leader's temporary absence.
More info on inactive clan leaders being swapped:
Inactive Clan Leaders
Locked account support page:
My account is locked
Your clan leader can try Tweeting @JagexSupport for more advice on unlocking the account.