How to allow advance leave to next year?

Go to eLeave > Leave Setup > Company Setup > Under Advanced Leave Policy

For Annual leave:

Untick the option: "Disallow annual leave application if no. of days applied is more than the current leave balance" 

For other leave types:

Untick the option: "Disallow non-annual leave application (other leave types) if the no. of days applied is more than the current leave balance"