How do I transfer data from iphone4 to iphone6 plus

Don't know what you mean by saying 'formatting laptop'. If you can't backup your iPhone 4 to iTunes, you're supposed to do a few things to make it:

1. Download and install the latest iTunes on your computer. You'd better download it from Apple official site
2. Launch iTunes, click Store menu to authorize the computer with your Apple ID;
3. Restart your iPhone 4 and try to connect it with your iTunes. If your iTunes recognize it and offer to set it up as a new device or restore, you should click set up as a new device. In the next step, you can see the option 'Back Up Now' to create a backup of your iPhone 4.

Besides, backing up iPhone 4 in iTunes and restore your iPhone 6 with the iPhone 4 iTunes backup to get the data, you can also backup your iPhone 4 to iCloud(tap Settings > iCloud > sign in with Apple ID > swipe iCloud Backup to ON and click Back Up Now) if your iPhone 4 can access a network. Later, on your iPhone 6, you can click Settings > iCloud > sign in with your Apple ID. Then tap Settings > General > Reset > Erase all content and settings. After then, set your iPhone 6 as a new device and there will be a 'restore from iCloud' for you. Then you can choose to restore iPhone 6 with the iPhone 4 iCloud backup.

If you still can't restore your iPhone 6 from iPhone 4 iTunes backup or you don't want to restore iPhone 6 from iPhone 4 iCloud backup, then try the easier way: using mobiletrans. It helps you to copy contacts, messages, videos, photos, songs, and calendar directly from iPhone 4 to your iPhone 6.