Regarding "extend" versus "expand the range" "extend" is completely general. It has no limitations. It means to grow something, but not necessarily in physical area. We can extend our sales into China. We can extend our product line into pharmaceuticals. We can extend the limits of our farm by buying our neighbor's land. We can extend our experiment by two months. "expand the range" sounds like a particular way of speaking that a particular person might prefer, but it is not more specific than "extend". There is no clear difference of meaning between the two, but I think there are situations where saying "expand the range" would sound strange. If you are not a native speaker, you should just say "extend". There is no good reason to ever say "expand the range" except maybe a few very specialized technical situations you can learn later.

“Expand the range” is usually used in connnection with economic activities or wildlife. Examples: The company plans to expand the range of its product offerings. Conservationists hope to expand the range of the endangered monkeys. Extend is usually used to mean “making something longer in time or physical length,” (example: He extended his stay in Shanghai by an additional three days”), to “reach out over a distances” (example: “the bridge extended over the river”), or to expand a program to reach more people (example: The government extended benefits to include an additional category of workers).