If your update is failed then automatically the update.zip gets deleted. We can reusE the saved update.zip
But it shouldn't be edited else this TUT will fail.
1) Check if you have /data/fota folder. Else create it and set permissions 700
2) Now copy our update.zip to that folder
3) Set permission of that file to 600
4) Now go-to software update and update as always
Now you are done. I saved 300mb data by this method.
PLEASE REFER TO THIS POST ON COPYING