If it will arrive later than that, I won't be needing the item anymore
If it will arrive later than that,
それ以上(到着が)遅れる場合は、
I won't be needing the item anymore
(商品は)もういりません
もう受け取るつもりはない、は直訳的に
I won't have the intention to take it anymore
とかになりますが、そういう表現はあまり聞いたことないですね。
もう要らない、送らなくていい（you don't need to send it to me anymore)などの表現の方が多く使われています。
ご参考になれば幸いです！
If the delivery date is going to be any later than sometime this week, then I won't be needing the item anymore.
If it's going to be delivered later than this week, I will not be accepting the delivery anymore.
ご質問ありがとうございます。
① "If the delivery date is going to be any later than sometime this week,"＝「もし納品が今週以降になるなら」
"then I won't be needing the item anymore."＝「もうその商品は必要ありません。」
② "If it's going to be delivered later than this week,"＝「もしも配達が今週以降になるのなら」
"I will not be accepting the delivery anymore."＝「配達はもう受け取りません。」
ご参考までに。
アメリカ合衆国 
