10w60 is the correct oil for the JTS, if that's what its used to then keep in on it.
Changing the oil is simple...
Warm the engine and get it up on ramps/axle stands (DON'T just use a jack, its not safe). Remove the undertray and locate the sump plug.
Undo said sump plug and allow the oil to drain into a suitable container until it stops running completely. Next locate the oil filter (back of the engine) using an oil filter strap, remove the oil filter, it will be full of oil so position the container underneath it to catch the oil. Allow the oil to finish draining fully.
Fit a new oil filter, making sure you use a little oil on the rubber seal, do it up hand tight.
Replace the sump plug, including a new sump washer, make sure its good and secure.
Now, crawl out from under the car, remove the oil cap and pour in 4.5l of 10w60 oil, then replace the oil cap.
Now get back under the car and replace the undertray, check for any leaks from the sump plug.
Get the car off the ramps/axle stands and check the oil level, adjust if necessary (to the max-mark on the dipstick, don't be tempted to overfill it).
Take the car for a drive, allow to cool and check the oil again.
Check your oil every week and keep it topped up to the max-mark on the dipstick.