open select>select using constraints now go into faces mode on your model and in the dialogue box choose 'all and next' and 'Nsided'. Now drag a selection over your model and only Ngons will be selected
Another method: (Polygons Menu) Mesh > Cleanup... Settings: Operation - Select matching polygons Scope - Apply to selected objects Fix by Tesselation - Faces with more than 4 sides Then click "Cleanup", it won't clean them up, but it will select them for you so you can decide what to do with them.