Does the rear sight have tritium vials that glow in the dark? If so, do they still glow pretty well?
If it has tritium vials and they still glow pretty well, I'd get a Glock rear sight tool to drift it over to your liking. The tools are pretty expensive though, if you plan on installing your own sights in the future it's a good investment but otherwise it may not be worth the cost.
If it doesn't have tritium vials, or the vials barely glow anymore, you can drift the sight over with a hammer and punch. Don't use a steel punch, use brass or even better a plastic punch.
When I installed the sights on my slide, I put the slide in a padded vice and used a hammer with a delrin(plastic) punch. I padded the gripping surfaces of the slide with cereal box cardboard taped on with masking tape. If you put the slide in a vice, you have to be very careful not to put pressure with the vice on the slide rails, the ejection port, or any portion forward of the ejection port. In order to do that properly without damaging the slide, you'll need to use small pieces of wood taped to the vice with masking tape, so that pressure is only applied to the slide in these areas:
Here's a good video showing sight installation, the only thing he does wrong is to put pressure on the slide with the vice on the ejection port area:
(he also uses red loctite which isn't my preference, the rear sight shouldn't need any loctite and I prefer to use blue loctite for the front sight)
Sights are a highly personal preference specific modification... In my opinion the Ameriglo Pro I-dots (w/ orange outlined front sight)are the best combat/ night sights available, and they also happen to be one of the cheapest options available at around $65. Good luck deciding!