How do i convert bigint to int in postgreSQL

I wanted to find out negative values in one of the columns of type bigint. so when i do select *from tablename where columname(bigint) <0 ... its throwing me an error.

Error:

SQL Error [42883]: ERROR: operator does not exist: bigint[] < integer Hint: No operator matches the given name and argument type(s). You might need to add explicit type casts. Position: 60 ERROR: operator does not exist: bigint[] < integer Hint: No operator matches the given name and argument type(s). You might need to add explicit type casts. Position: 60

Please help.