need more storage for update

Look at Settings > General > Usage. It will tell you the large space consumers.

Any movies or TV shows transferred from your iTunes library take up quite a bit of storage space and can be re-transferred after the update has been installed. If your iPhone's Camera Roll includes a lot of photos/videos, import those with your computer followed by deleting from the Camera Roll after the import process is complete. The imported photos/videos can be transferred back to your iPhone via the iTunes sync process after the update has been installed.

Delete apps rarely if ever used which can be reinstalled after the update has been installed.

laudrain wrote:

Best things to delete for more storage for update?

Delete nothing. Just update via iTunes on your computer. You won't have to remove data from your iPhone to update your iOS that way.