The 32-year-old came off the bench to score twice in eight minutes, his first goals since January, in the 4-0 EFL Cup win over League Two Yeovil.
"It is a very important competition. We have a big squad and I think this year we have to improve and these two (Williams and Bolasie) will help the team improve as they are very good players," he said.
"We have a very good manager. I knew him before and played with him in Holland at PSV and he will improve us.
"I think this year we have a big squad to do more and improve and to finish very high in the table."