Increase memory of a particular vagrant box

I have this Vagrantfile. Here I defined the memory to be 2048 for all VMs. But I want my puppet master to have 4096 and agents to have 2048. How to do that?

Vagrant.configure("2") do |config|
  config.vm.synced_folder ".", "/vagrant", type: "virtualbox"

  config.vm.provider "virtualbox" do |v|
    v.memory = 2048
    v.cpus = 2
  end

  config.vm.define "puppetmaster" do |pm|
    pm.vm.box = "centos/7"
    pm.vm.network "private_network", ip: "192.168.33.10"
    pm.vm.hostname = "puppetmaster"
  end

  config.vm.define "puppet-agent-centos" do |pac|
    pac.vm.box = "centos/7"
    pac.vm.network "private_network", ip: "192.168.33.11"
    pac.vm.hostname = "centos-agent"
  end

  config.vm.define "puppet-agent-ubuntu" do |pau|
    pau.vm.box = "ubuntu/xenial64"
    pau.vm.network "private_network", ip: "192.168.33.12"
    pau.vm.hostname = "ubuntu-agent"
  end
end

Thanks!