How to join a domian through Control Delegation

hello dear fellows

i have two OU name , CompanyUser contain simple user and an other OU name Support, Support OU can two user that are responsible to join the domain, intall the software, configure the printers etc,,

i create a Security Global group name Support
user member of this OU login domin contrller
but when thay are going to join domain on other computers the “change” option is grayed

any one have an idea???
how i fix the problem???

thankx in advance