Upgrade of plan is allowed however it doesnt come with the unit, theres no offering yet similar to the Iphone 5 early recontracting.
But if you still want to avail the s4 while keeping your current number, you'll need to pay for the handset based price of the unit you previously availed (100% or 50%) depending on the lenght of you contract.
or you may apply for an additional line+phone provided that your credit limit or your financial document will suffice the additional plan you will be availing.
@qtmashi upgrading of plan is possible as what demerok has said but it doesn't come with a Free handset. If you really want S4 you can tweet @talk2Globe or call the recontracting department to check how much would you need to pay if you are going to avail the S4 under recontracting. You must also check when will your Plan was availed and how many months remainig before the contract ends, another possible solution is to terminate your current plan then apply a new one. Both option has corresponding fees and computation.
To give you an idea for termination payment: 50% of the unit price if the remaining contract period is below 1 year while 100% of the Unit price if beyond 1 year
Remaining Months in the Contract: 15 Mos
Handset Price (No. of months remainig on the contract/No. of months of Contract)
Sample: S3 Handset
31000x(15 months remaining on your contract / 24 Months Lock up Period) = Php19375.
You need to settle Php19375 to terminate your current account.