This is a good translation but the paragraph states "at least" (por lo menos) 30 days before the cancellation not "within" (dentro) and the phrase "to the other party" must be included.
I think cancel
is the better choice over anull; and intention
is the better choice over will.
Here is my suggestion:
Notwithstanding the previous article (3.1) any of the parties has the full right to unilaterally cancel this contract it in its entirety, without penalty, by communicating their intentions, at least 30 days prior to the date of cancellation, by any proper written means to the other party(ies).