Can't update installed programs after purchase of my iMac

Hello everybody,

I can't update the programs that were installed when i bought my iMac.

For example: Pages, numbers and keynote were installed by apple when I received my iMac. Now I get the message that there is an update available, but it doesn't update. I receive a message that I should be logged in with the same account as I bought them. Problem is that I just have 1 account.

Can anyone help?

Thanks

Ruben