Engine noise- oil?

I have a  97 lantra 1.6 gls and has 180k miles on it . The engine started to make a nasty clicking noise recently its loud, and there continously. Ive heard changing the oil helps but this is my first car and I dont have a clue so any help will be great ie: what is the best oil to use. 

At this point you probably want to buy one of the oils specially formulated for high-mileage cars.  Make sure it meets all oil requirements (viscosity, etc.) for your car.  Is it the engine itself, or might it possibly be the exhaust manifold?  Sometimes an exhaust leak can sound like a ticking noise.  If that's the problem, it's a relatively straightforward fix.  If it's the engine itself, your engine is probably getting ready to die (although it might last quite a bit longer before it goes).

Thanks for the help. I put 15w/40 in and after a few days  its quitened down . but now it seems to be overheating, any ideas? It cools down when I put the air condt. on full heat.

Check to see if your cooling fan is coming on.  If not, you might have a problem with the fan or its controls.  I just fixed this exact problem on my 1995 Escort for less than $10.