Depends on your attitude towards the Bible.

If your attitude is religious, than you can simply say that we don not know God’s ways.

If your attitude is historic, than you can say that we cannot take the Bible always verbatim, and maybe the giants mentioned in the Bible are some far mythological residues that slipped into by the Bible authors.

If you are very creative you can attribute the giants to some extraterrestrial life.

Decide for yourself.