You can change the letter spacing in CSS by using the “letter-spacing” property. You can either increase or decrease the spacing by specifying the value in pixels(px), points(pt) or em.
For example:
```
p {
letter-spacing: 2px;
}
```
This would increase the letter spacing in a paragraph by 2 pixels.
If you want to decrease the letter spacing, you would set the value to a negative number. For example:
```
p {
letter-spacing: -1px;
}
```
This would decrease the letter spacing in a paragraph by 1 pixel.
