How to fix my DS4 controllers myself?

So, I've had this problem for awhile, but am just now looking at actually fix it (if possible). Basically, both my DS4's have some sort of problem with the sticks. One of them, for instance, gives bad input-- I'll be moving straight to the right in something like the Binding of Isaac, and every so often Isaac will dip downwards, then back straight. This is the more heinous and messes up a lot of inputs, pushing me back when I'm aiming straight, so on and so forth.

The second controller just has a bit of a problem with the R3 and L3 click, for sprinting and whatever it's used for in other games. Sometimes it just doesn't register until I push really hard. What can I do to fix these? Can I crack these open and fiddle around with them myself, or is this something I should just replace?

Thanks in advance.