You can adjust the pressure against the Delta ball valve by simply removing the handle (Allen wrench), inserting the tips of a pair of needle-nose pliers in the two slots of the white plastic ring around the inside of the ball cover, and slowly turning the adjusting ring clockwise until the leaking stops.
You don't even have to turn the water off for this adjustment. In fact, you want the water and the faucet ON so that you can see when it stops leaking as you adjust it.
Don't over-tighten the adjusting ring because it will make the handle too hard to operate.
If adjusting doesn't do it, it just needs new seats-and-springs (that seal against the ball inside the faucet), which are inexpensive and easy to install. We can walk you through that, too. Use only Delta parts.