There is no need to become an LPN prior to seeking your RN. You can become an RN by completing any pre-licensure program (diploma, associate degree or bachelors degree). In the US, most hospitals prefer BSN graduates. Then you have to pass the national licensure exam (NCLEX) in order to be an RN (all graduates, no matter what the degree, take the same exam). In the US, all RN new grads are 'generalists' - trained to begin work in any clinical area. After you have your RN, you can then work toward specialty training.
Nursing programs differ in their requirements for admission. You didn't provide much information about yourself. I would advise you to talk to admissions advisors for nursing schools in your area to explore their requirements for and admission process.
Wishing you the very best -