When you first enter the null you will find Trixie who will tell you how to upgrade.
Tips and tricks to upgrading.
Personally. I would upgrade all the rings I have equally so I will have a stronger ring balance. Some people like to stick with the basics and level up only one ring at a time. Its all in what you feel best.
Click R to open the inventory
Now you can equip whatever rings you may have picked up already if you have that is. In the inventory there is a tab called rings which should already be open. Drag and Drop the rings of your choosing next to the Guns Guns Guns ring.
Alright now its time to upgrade your rings. Click on the Guns Guns Guns ring. In the inventory is the status of your ring. Click on upgrade. You see that it takes the purple charge orbs you have been collecting to make the ring more powerful. Continue to upgrde until level 2.0 or higher if you want. Upgade however you want.
If you do not want a ring and you have multiple rings on you simply hit Salvage. It will give back some charge orbs.
Swaping Charge levels with other rings only last for 24 hours if you salvage any ring under this it will not change back the charge level.
As you can see there are purple crystals sticking out of the ground. These re ways to jump from place to place like you did when you got here. Try to find all the null crystals in each map on your own or as someone in the game to help you get to them.
Close out of your inventory and click on the crystal of your desiered location.
Hint: Trixie will give you some in game advice on anything and everything. When you daze or visit the null.
And of course people can comment on how they feel about the ring sets they have and other things. Just feel free to explore what you discover in the rings along the way and explore other peoples ideas. Couldn’t hurt to try new things every now and then.