The first two questions are very similar. "What should I call you?" is more polite than asking "What can I call you?" but the meanings are the same. These questions are much less common than "What is your name?"
"How can I call you?" is the way you might ask someone for their phone number. "How can I call you," is similar to "How can I get in touch with you?"
If you'd like this to be explained in Spanish, just ask!
