Hi and Welcome !
Is the computer you are using your own computer ?
If no, it is probable the the 'owner' has it set up so that only the 'Administrator' can make changes to the system.
Installing a program is a big change, right ?
When you first start the computer what do you see on the screen ?
(No need to tell us any names !)
Do you need to click on anything and maybe also enter a 'password' ?
And, er, ummm... Are you allowed to use the computer ?
Need some answers before more help can be offered...