Given a grammar which is LL(1), it is easy to use an LL(1) parser generator. It is even easy to write an LL(1) parser generator.
If the underlying language is LL(1), but the grammar is not , that is, it contains left-recursion or common prefixes, then the grammar must be changed, a fairly complicated process.
If the underlying language is not LL(1), however, bottom-up parsing techniques may need to be used.