Change admin account

Hi SanYang , 
yes you can 
( Go to system >>> Users >>> Choose " Michael "Account >>> in Role drop down list >>> Choose Administrator ) 
to do that you shoud login with the admin account or another account has the administrative rights. 

Also you can disable the baisc system default admin account , but I don't prefer that 
if you want to know the way to disable it let me know. 

Hi SanYang , 
Create the new account first let we say ( Michael >>> Password "xyz@123" >> Role "Administrator ) and it's optional to allow CLI accress for this account you can enable advanced shell or tmsh. 

After creating it , 
Logout and login again with your new account " Michael " 
then 
Go to ( System >>> Platform ) , 
then at admin Account field >>> Select disable default account , use alternate. 
you have done it now. 

for detaild steps , Check this Article : 
https://my.f5.com/manage/s/article/K15632#disabling

it contains video clarify how to do that. 

thanks