Nkumu and James-Lewis leave U's.
Boss Joe Dunne is busy making plans for his first transfer window in January and, having already sent Tom Bender and Bradley Hamilton out on loan to Chelmsford, he has now made the decision not to keep Merrick or Archange at the U's in the longer term.
Speaking about former Southend man Merrick, who featured regularly in the U21s this season, Joe said: "His contract was up at the end of this month and I have decided to not renew it.
"As I've said before, with the lads in the U21s I need to look at how their progression is going in getting towards the first team and Merrick was some distance from that side.
"Letting him go now gives him a chance to find a club in the January window."
Teenager Nkumu came to the U's from Chelsea as Joe took the chance to take a closer look at the young midfielder in the U's U21s fixtures.
However, he is now back with the Premier League side.
Joe added: "Archie struggled with injuries during his time here. He's technically a good player, given his Chelsea background, but he found it difficult here.
"He's been a good lad, who was willing to do well, but it's not kicked off with us and I need to move on.
"I made the decision that he goes back to Chelsea and I will now look to recruit elsewhere."