How often change spark plugs 2007 Toyota solara?

Check your owner's manual. The Iridium tipped plugs used in most late model engines don't need changing for 100 thousand miles. That's a good thing since (on the V-6 anyway) the rear plugs are a little tough to reach.

If yours is the V-6 here's something to consider. The cam drive belt is scheduled for a change at 90 thousand miles. Since so many items are removed for that service anyway it makes sense to change the plugs and water pump at that point.

Cheers