You can update the default GAL like so:
Update-GlobalAddressList ‘Default Global Address List’
If you want to update ALL address lists:
Get-GlobalAddressList | Update-GlobalAddressList
Update-OfflineAddressBook “Default Offline Address Book”
Update-FileDistributionService %replace with the name of your mailserver%
Get-OfflineAddressBook | Update-OfflineAddressBook
Get-GlobalAddressList | update-GlobalAddressList
Get-AddressList | update-AddressList