Assuming that the over in the first being missing from the second is an error, they already mean the same thing, practically speaking. What makes them different at this point is simply the word over.
The first means that you went to a beach party at some point in your life, more than a year ago, and haven't been to one since. The second means that you went to a beach party a year ago, and haven't been to one since.
You can replace been with gone in the first example without changing the meaning, though depending on dialect it may come across as less formal.
You can replace went to with was at a beach party in the second one with only a very, very minor change in possible meaning, and most people would consider it to mean the same thing.
You can change the first to have that same subtle difference in meaning by replacing been to with been at.
The subtle difference in meaning is that "been/gone to" or "went to" suggest that you had to actively go to it, that you had to physically move to go to it. With "been at" or "was at", that implication is not there. Except for the fact that most people will see the meaning as identical anyway. If you try to claim that you didn't "go to" a party because it was at your house, you will seem an insufferable pedant. "I didn't go to the party, it came to me" might be lovely as poetry or philosophy, but in terms of day-to-day meaning it just seems fussy.