If your engine is making noises now, you might want to check that out before you change oils. As a Mechanic with over 25 years behind me I can tell you about oil.

10W30 What does that mean?
10 = the flow rate
30 = viscosity

That is the break down for all multi viscosity oils, 10W30 oil has the viscosity of a 30W oil and flows like a 10W oil.

except ! 10W40 or 40W

YOU SHOULD NEVER USE 40W OIL IT IS NOTHING MORE THAT 30W OIL WITH ADDITIVES THAT CAUSE SLUDGE !!!!! 15W40 excluded !

15W40 is a diesel blend and should only be used in DIESELS !

Synthetic or conventional
with conventional oil you should change your oil about every 5000 miles. depending on your driving conditions.
I change my oil every 10,000 miles weather it needs it or not. All of my vehicles have over 200K and 1 with 320K

With the synthetic the benifit is that it incapsulates dirt, so it gets caught in the filter. Actually if you compare the cost of the oil changes that you would skip with the synthetic the cost will come out the same

Personaly I do not recomend synthetic oil for a few reasons.
If it is a blended synthetic than it still has conventional oil in it !
Synthetic oil will seep where conventional oil will not, yes you will leak.
The cost and availability of full synthetic for top off.

The thing that everyone is MISSING is the filter ! It really don't matter how good your oil is your filter is what protects the engine by trapping the dirt.

As I said before I change my oil religiously every 10K miles I use CASTROL oil and WIX filters, NAPA filters are made by WIX

I also use K&N air filters, and you can forget you have an air filter, DONE