Can I change my field for Masters?
That depends on the requirements / prerequisites of the specific program you are applying to, but Masters classes assume you already understand the topic at a Bachelors level and unless you have at least a strong minor in that area you are unlikely to succeeded and thus unlikely to be admitted.

A better approach might be to ask schools if they would let you use any part of you existing degree as "transfer credits" toward a faster Bachelors degree,  then continue from there to the Masters.  You might be able to complete the new B in three years, or even two, if you have good enough grades in material that overlaps their program.