Japanese Grammar

I'm a little confused with to narimasu as when to use it. Normally, I use ni/ku narimasu for noun and adjective, but for to narimasu I'm not sure at all.

Never use 〜となります. It is used by some people/businesses to make it sound like they are not responsible for some inconvenience to customers when they totally are. E.g.,

お支払いは現金のみとなります。

This makes it sound like they accept payment by cash only due to some natural law, rather than because they want to avoid the costs involved in accepting other payment methods. Rather, say

お支払いは現金のみです（でございます）。

P.S. : please use more descriptive titles for your questions; one should be able to know what a question is about without opening it.

When we mean {alpha becomes beta} or {alpha changes into beta},
mostly "ni naru / nari-masu" is preferred:
Alpha ga beta ni naru / nari-masu.

e.g.

(1) Here "to naru / nari-masu" is not suitable.
[JA] Shingo(h) ga ao ni nat-ta.
[EN] The traffic signal has turned green.

When "to naru / nari-masu" is used,
it may imply that {alpha is to be beta} due to a rule, a situation, a circumstance, etc.;
the speaker thinks or insists that this fact is natural, inevitable or irresistible.

e.g.

(2) Here "to naru / nari-masu" is more suitable.
[JA] (Senkyo no kekka,) kare ga atarashii shicho(h) to nari-masu.
[EN] (As a result of of the election,) he is to become the new mayor.

(3) Here whether "ni" or "to" makes almost no difference.
[JA] Kanojo wa boku no hanayome ni | to naru hito desu.
[EN] She is a person who will become my bride. | She is my bride-to-be.