First I will cover some of the effects that can be caused by incorrect peep height
Peep too low;
Crunching down and tilting of the head and neck giving rise to poor form and potential muscle and skeletal problem
Excessively high bow shoulder
Peep too High;
Overextension/stretching of neck and shoulders
Floating/inconsistent anchor point as there is inadequate or no contact between hand and your locating point on jaw
As you can see both conditions are detrimental to your shooting performance and can also lead to some forms of Gold fever/Target panic as these inconsistencies play on your mental and physical form.
Step one check your Bow setup and shooting form;
a) Set correct arrow rest height and center shot (under shooting tips on this site)
b) Set you nock height
c) Examine your anchor point for repeat-ability of placement and solid relaxed feel
d) check on your form by briefly running through the Shooting basics page on this site
Step two checking your Peep;
a) Draw your bow in front of a target using your best form with an arrow in to avoid the chance of a dry fire and as you are coming to anchor close your eyes, settle into position for the shot then open your eye looking through the sight if too low you will be looking over the peep.
b) Move peep in the correct direction and Repeat this process until your peep lines up with your eye when you open them after settling in for the shot
c) As you will have moved the peep along the twist of the string you will probably need to use a bow press to align your peep by rotating it or a partial twist of the string to get a clear view, as the use of a bow press can be dangerous please seek assistance if in any doubt!!!
d) Moving the peep up will move the impact point of the arrow up for any given sight setting and conversely lowering the peep will lower the point of impact so your sight settings will require re setting.