Not only is this possible, but it is preferable. You will generally save up to 70% of your energy costs by doing so.
Do be aware that when you replace your old halogen lights with LED lights, they must be compatible with both the fitting and the lamp base. A 12V halogen lamp can for instance have a G4, GU5.3, or G53 lamp base.
A 220V halogen lamp can for instance have a GU10, E14, or E27 lamp base.