Syncing setup cannot be changed on the fly. Changing anything about syncing usually requires changes be made to every machine that is participating.
The way to make any changes to a syncing configuration is on the primary machine you stop syncing - the primary machine is the only one that will give this option.
Delete any data from Dropbox and wait for it to sync. The primary machine at this stage should be in a state where it thinks it is a standalone system so you set up syncing on it from scratch.
The data that is on any secondary system cannot be linked back to the primary, it is effectively an orphan, but at this stage I tend to rename it and have it in a safe place just in case anything goes wrong, you then set up any secondary machine as you did when you initially set it up.
At some later stage yo can delete any old data files that are on the secondary machines.
So what you are really doing is stopping syncing and then setting it up from scratch again. That is the only way of changing any details that relate to it.