Understand that the charge of an atom depends on the balance between protons (positively charged) and electrons (negatively charged).
Recognize that protons are fixed in the nucleus and do not change during typical chemical processes, so gaining or losing protons is not how atoms become charged.
Know that neutrons are neutral particles and do not affect the charge of the atom, so losing or gaining neutrons does not change the charge.
Realize that an atom becomes positively charged (a cation) by losing one or more electrons, which reduces the negative charge and leaves the atom with a net positive charge.
Therefore, the correct way for an atom to become positively charged is to lose one or more electrons.