@Daniel If you're on Prepay and you want to move to the All You Can Eat Data €20 plan then, yes. You can pick up a new Prepay SIM with an 083 number attached in any Three Store or online Here When you get that SIM then you submit this form to move your number to the new SIM Here
You'll be on the All You Can Eat Data plan
If you want to ask me any question on your current number and account just click on the "Send me a PM" link in my signature. Hope this helps!