I currently have an iphone 5s on verizon with unlimited data. I have an upgrade on this line so if i use it will i loose my unlimited data? How can i keep the unlimited plan ?
You'd have to buy the phone full price to keep unlimited. There are a few work arounds but I wouldn't do them if you really don't want to risk unlimited data.
Check our Verizon Forums to read up on a few work arounds if you want to try them.