Someone from their hotline said that subscribers will be migrated automatically but still I applied for an upgrade through their hotline.
If you're on a contract, it won't change until the expiry. It is considered as a new contract if you opt to update your current plan with a better subscription. You'll have to pay the termination fee and re-contract again.
But if you're out of contract (24 mos I believe), you can notify them for changing of your subscription. They won't update it automatically.
Just to add, currently we switched from Globe DSL's 1299 3mbps unlinet to PLDT's DSL/Fibr connection. Now enjoying 10mbps of unlimited internet (literally without data cap) for 1799/month.