Okey-dokey, here I go.
The stats in both of my tanks are this:
Nitrate- 40
Nitrite- 0
hardness- 300
alkalinity- 300
pH- 8.4

I was told that a water change would help to lower the nitrite, and it did. My mom told me that adding some aquarium salt would help soften the water, so I put some in and it didn't help. I was also told that adding driftwood to the tank decor and it would lower the pH. I'd like help lowering the hardness and alkalinity.
Straight from the tap is:
Nirtate- 0
Nitrite- 0
hardness- 300
alkalinity- 300
pH- 8.4

Help please.

You really don't need to lower KH, GH or pH. Your readings are find for goldies. Driftwood may lower lower pH over time, but it may not, cuz your water is well buffered.

Aquarium salt won't soften the water. Tho, it will help protect against nitrIte poisoning.

So how long has your tank been set up?

The 10 gal has been up for almost a year and the 29 gal has been up for a little over a month. Both have cycled and both have fish in them.