2 bit saturating counter
It depends wether the counter is signed or unsigned. Let's say it is unsigned. So the possible values, in up sequence, are 00-01-10-11. 00 is the minimum and 11 is the maximum.

Let's take state 10. If a count-up is received, it goes to 11. If a count-down is received, it goes to 01. 

Now let's take 00. If a count-up is received, it goes to 01. But if a count-down is received, it stays at 00.

Analyze the other states similarly and complete the design once you have all the states and next states transitions.