Meu espaço em disco está cheio e continue recebendo mensagem de alerta.
Será possível adicionar um disco rígido extra ou alterar o disco rígido aumentando o tamanho no meu MacBook?
My disk space is full and keep getting alert message.
Will it be possible to add an extra hard disk or change the hard disk by increasing the size on my macbook?
Most probably yes. Almost all MacBooks, except for some newer ones, have upgradable storage. If you want to see if you can upgrade yours, I would look up your MacBook on EveryMac.com. It uses your serial number, which can be found by clicking the Apple logo on the left end of the menu bar, and selecting "About This Mac".
Once at EveryMac.com, scroll down to the Storage selection where it will specify if it can be upgraded. Alternatively, you could Google your MacBook once you've identified it.