How can I decrease the threads while running jMeter?

I create a test plan when working with jMeter, and I want to create a test plan with 100 concurrency users.

After first page(homepage) I want to decrease 50 users(drop-off and do not access to next page) while 50 another users continue access to another page.

Someone suggested me use Ultimate Thread Group but I think it can't help.

Any idea for this issue?