For NDetG -> DetG, you can always use the subset construction after removing the unsafe states.
For NDetF, that is not always possible, at least it works for totally defined automata, and sometimes also for others, which is however not that easy to decide. The safe way for NDetF is therefore to convert it to NDetFG and to use the breakpoint construction to get a DetFG automaton. Note that some NDetF automata do not have equivalent DetF automata at all.