Here is how to upgrade spawners:
1st tier/bronze: To upgrade the first tier spawners you will need to have the amount of money required and the amount of bronze fragments that are required(Which is one).
Pig: 20k
Wolf: 25k
Ocelot: 30k
Rabbit: 45k/1 bronze fragment
Chicken: 60k/1 bronze fragment
Sheep: 80k/1 bronze fragment
Cow:120k/1 bronze fragment.
2nd tier/silver: To upgrade silver spawners you will need to have the amount of money required, and the fragments that are required.
Mushroom Cow: 200k/1 silver fragment
Cave Spider: 250k/1 silver fragment
Zombie: 330k/1 silver fragment
Skeleton: 350k/2 silver fragment
Creeper: 450k/2 silver fragment
Slime: 650k/3 silver fragment
Blaze: 800k/3 silver fragment
3rd tier/gold: To upgrade gold spawners, you will need money and gold fragments.
Guarding: 1m/1 gold fragment
Enderman: 1.5m/1 gold fragment
Iron Golem: 2.5m/1 gold fragment
Pigman: 4m/2 gold fragment
Silverfish: 8m/2 gold fragment
Villager: 10m/3 gold fragment
Ghast: 13m/3 gold fragment
So I listed all the prices of the spawners and what's required to upgrade them, but remember, you'll need 100 of each to upgrade them to an epic spawner. To upgrade a spawner, you can just right click on it, go to the prestige spawner, make sure you have the requirement to upgrade, and then press yes. You don't need SkyVip+ to upgrade spawners. You do however need SkyVip+ to mine them, or you can purchase a Seasonal Silktouch Voucher or a Silktouch Voucher. And if you want to combine to epic spawners, yes, I do believe you would need to mine it and place it next to the other epic spawner so they combine.