To get used to the altitude you could follow some of these recommendations:
Rest the first day in the altitude
Drink more water
Drink Coca tea
Eat light food
Consult in your pharmacy the best medicine for Altitude disease
Note: The symptoms of altitude sickness can be felt at different altitudes (approximately from 2000 meters high), it depends of each person. Usually some of the symtoms are difficulties to breath, headache, dizzeness, vomiting. Drink water before going to high altitudes should decrease the probabilities to get altitude sickness.
If you want to go hiking in the Andes, it is recommended to start with a full day easy hike. In this site you can find many options for a good acclimatization.