In case of low physical memory availability, investigate what is the cause of it, by analyzing sap hana peak memory usage processes.
If memory shortage alerts still appear on your sap hana system after having sorted out peak memory usage events, start thinking at ways of upgrading your system with: New Allocation memory threshold (Sap License), new physical memory (RAM), looking at a migration to a new Server.
Between available budgets, decisions, planning and work involved, getting to a migration project is something which will take few months.
Getting a new sap license deal on new memory extension could take a while as well as purchasing new physical memory, but those 2 types of upgrade can happened within weeks.
-- Free physical memory size
DECLARE V_INSTANCE_NAME varchar(20);
select t1.VALUE into V_INSTANCE_NAME from "SYS"."M_SYSTEM_OVERVIEW" t1
where UPPER(t1.NAME) = 'INSTANCE ID';
select V_INSTANCE_NAME as Instance_id,
round(FREE_PHYSICAL_MEMORY/1024/1024/1024, 3) as "Free Physical GB Size"
INSTANCE_ID Free Physical GB size