Yes you can .. It is a best offer.. But there is terms..
Once the SIM is upgraded to a 4G SIM customer can continue using his/her existing mobile number
FREE Data up to 5GB offer,
Valid only once per SIM upgrade
Valid for Any Time Internet surfing/usage
Valid for customers upgrading their existing SIM to a 4G SIM during the promotional period
Once SIM upgrade is completed, FREE Data up to 5GB will be allocated within 24 hours
Not eligible for customers on unlimited data package
Other Dialog Mobile/Mobile Broadband terms and conditions apply