How often or at what mileage should I change the spark plugs on my used Ford Expedition...?

I picked it a year now, and I am wondering if I should get it down now.........How often or at what mileage should I change the spark plugs on my used Ford Expedition...?The manual recommend 100K miles, but I wouldn't go that far. I would do it around 50K to 75K miles. Imagined how hard it would be to remove it from engine block after so long. Replace it and have a peace of mine..How often or at what mileage should I change the spark plugs on my used Ford Expedition...?A buddy and I were just talking about this and I would say about every 50,000-60,000 miles, if you just got it though and it never had a tune up depending on the mileage then yeah, it can't hurt should run better maybe get better gas mileage.How often or at what mileage should I change the spark plugs on my used Ford Expedition...?if you buy a manual it will tell you how oftem , i do it once a year