Simplify the following text for a Grade 12 native English-speaking person.
Original: All insects in the Pterygota undergo a marked change in form , texture and physical appearance or metamorphosis , from immature to adult . These insects either have hemimetabolous development , and undergo an incomplete or partial metamorphosis , or holometabolous development , which undergo a complete metamorphosis , including a pupal or resting stage between the larval and adult forms .
Simplified: There are two main types of metamorphosis in insects : incomplete metamorphosis or hemimetabolism , and complete metamorphosis or holometabolism .