– Decreasing (DEC) –
Decreasing in your crochet basically means reducing the number of stitches. Hereby the circumference or width of your project will be shorter.
If you want a smooth transition, often you reduce two stitches to one. However you can also come by patterns, where you have to reduce working over three or four stitches.
The below example is decreasing from two stitches to one in single crochet.

Instructions
Decrease Single Crochet (DEC SC):
Push your hook through the “V” – place yarn around the hook and pull back through the “V” – now push your hook through the next “V” – place yarn around the hook and pull back through leaving three loops on your hook. Place your yarn around the hook and pull through all three loops.


Place your yarn around your hook – push your hook through the “V” – place yarn around the hook and pull back through the “V” – now push your hook through the next “V” – place yarn around the hook and pull back through leaving four loops on your hook.
Place your yarn around the hook and pull through all four loops.
Place your yarn around your hook – push your hook through the “V” – place yarn around the hook and pull back through the “V” – now push your hook through the next “V” – place yarn around the hook and pull back through leaving four loops on your hook.
Place your yarn around the hook and pull through three loops.
Place your yarn around your hook and pull through the remaining two loops.

Decreasing in other stitches more or less follows the same instruction. If the instruction is different, you can find it included on the page of the stitch.
Alternatively if you wish to add length to your circumference or width, you increase the number of stitches. Please see my instruction on increasing stitches HERE.