4 KClO3 (aq) → 3 KClO4 (s) + KCl (aq)
This is an oxidation-reduction (redox) reaction:
ClV + 6 e- → Cl-I (reduction)
3 ClV - 6 e- → 3 ClVII (oxidation)
KClO3 is both an oxidizing and a reducing agent (disproportionation).
This is a precipitation reaction: KClO4 is the formed precipitate.