How adjust ballcock in my attic

Amateur here!
See photos. The cold water tank is my attic is constantly dripping (a drop every 5 seconds) onto the outside of my house.
It seems fairly obvious that I should adjust the ballcock in my water tank.
I have done this sort of thing before but in my toilet cistern. It seemed simpler to do in my toilet.

It is not clear to me how I adjust the ballcock. No obvious place to screw/unscrew etc.
I have included numbers in my photo as it may help you to explain!
Thanks folks.

 

[ShaunCorbs]

If it’s dripping it needs a new washer or to be honest best outcome is a new float valve

 

[Kirkharryhillsalter]

As mentioned above your best action is to purchase a replacement ballcock washer kit , strip it apart , remove and replace the sealing washers this isn't as simple as it sounds for a novice ,if I were you I would purchase a new part 1 valve & float and before you actually install it the float arm normally needs a slight bend roughly 25⁰ down if you have a blowtorch I'd recommend removing the plastic float then heat up a 3 inch section of the brass arm roughly in the middle until it turns a dull red at that point quench it in a bucket of water or cool it somehow really fast this action will make the brass arm easier to bend ,then bend it ,see Utube there are hundreds of videos for clarification then before you install the valve I'd recommend completely drain the tank it's going in ,I'd wipe the inside with blue roll tissue once empty then use a very very dilute bleach solution on a cloth this will kill any bugs in the tank as some of them can make you very sick
Before you start watch as many UTUBE videos as possible until the process makes sense .
buona fortuna amico mio 🫡

 

[MikeJhn]

Before you do any of the above push the float down below the water level to flush what may be a bit of dirt on the washer, note you will get water flowing out of the overflow which in turn may impact a path and in this weather may freeze and become a hazard.