It's easy. We predrilled holes to attach the brackets. When you measure your windows, measure the top, middle and bottom and go with the smallest measurement. Do your length like that too but take the longest measurement.
Lowes does come out and measure along with install. I've noticed the prices are based on the area you live. When I worked at Lowes in the blinds when Bali would do a sale and we had people who we did measurements for, we would call twice to let them know of the promo. Many times it was like a week before the promo kicked in. If you have to order, go with Bali. Especially if you are going to be there for a while. They have a lifetime warranty and you call them with the order number in the headrail and they send out what you need.
When we put our house on the market a wood tassle broke and a blind broke and they replaced it all with no issues.