https://support.apple.com/kb/DL2000?locale=en_US
Instead of doing it through software update, try downloading the update from this link then install it.
Installation failed. Log output:
2019-06-01 11:07:47-04 MacBook-Pro softwareupdated[359]: bridgeOS: Minimum bridge version requirement satisfied (16.16.5125.0.0,0), skipping search for bridgeOS update
2019-06-01 11:07:47-04 MacBook-Pro suhelperd[360]: Verifying package at path: /Library/Updates/_ManualUpdate/macOSUpdCombo10.14.5.pkg
2019-06-01 11:07:47-04 MacBook-Pro suhelperd[360]: packageWithPath returned nil!
2019-06-01 11:07:47-04 MacBook-Pro softwareupdated[359]: SoftwareUpdate: request for status for unknown product _ManualUpdate
2019-06-01 11:07:47-04 MacBook-Pro softwareupdated[359]: Package Authoring Error: PackageInfo bundle reference found without top-level bundle definition. Bundle will be skipped: <bundle id="*"></bundle>
2019-06-01 11:07:47-04 MacBook-Pro softwareupdated[359]: SoftwareUpdate: Personalizing manual product at /var/folders/zz/zyxvpxvq6csfxvn_n00000s0000068/C/com.apple.SoftwareUpdate/localhost/AdoptedManual/macOSUpdCombo10.14.5.pkg
2019-06-01 11:07:47-04 MacBook-Pro softwareupdated[359]: SUPersonalizationManager: Enqueuing personalization request
2019-06-01 11:07:47-04 MacBook-Pro softwareupdated[359]: SUPersonalizationManager: Starting personalization
2019-06-01 11:07:47-04 MacBook-Pro softwareupdated[359]: SoftwareUpdate: request for status for unknown product _ManualUpdate
2019-06-01 11:07:47-04 MacBook-Pro softwareupdated[359]: Package Authoring Error: PackageInfo bundle reference found without top-level bundle definition. Bundle will be skipped: <bundle id="*"></bundle>
2019-06-01 11:07:47-04 MacBook-Pro softwareupdated[359]: SoftwareUpdate: request for status for unknown product _ManualUpdate
2019-06-01 11:07:48-04 MacBook-Pro softwareupdated[359]: Package Authoring Error: PackageInfo bundle reference found without top-level bundle definition. Bundle will be skipped: <bundle id="*"></bundle>
2019-06-01 11:07:48-04 MacBook-Pro softwareupdated[359]: Personalization summary: 18E226 -> 18F132 (Customer), global = 0, variant = multiple, client = softwareupdated, user auth = 0, tdm = 0, prod fused = 1, model = j132ap, session = 8504F3D6-1201-43B3-9440-E5958B3858EF: Error Domain=OSPErrorDomain Code=302 "The signed AP ticket could not be found." UserInfo={NSLocalizedDescription=The signed AP ticket could not be found.}
2019-06-01 11:07:48-04 MacBook-Pro softwareupdated[359]: SUPersonalizationManager: Personalization failed for _ManualUpdate: Error Domain=OSPErrorDomain Code=302 "The signed AP ticket could not be found." UserInfo={NSLocalizedDescription=The signed AP ticket could not be found.}
2019-06-01 11:07:48-04 MacBook-Pro softwareupdated[359]: SoftwareUpdate: Could not personalize manual product at /var/folders/zz/zyxvpxvq6csfxvn_n00000s0000068/C/com.apple.SoftwareUpdate/localhost/AdoptedManual/macOSUpdCombo10.14.5.pkg
2019-06-01 11:07:48-04 MacBook-Pro softwareupdated[359]: Manual product is nil, therefore an error occured, stashing token will NOT be created...
2019-06-01 11:07:48-04 MacBook-Pro Installer[4173]: ManualAdoption: Error adopting /Volumes/macOS 10.14.5 Update/macOSUpdCombo10.14.5.pkg: Error Domain=SUErrorDomain Code=700 "Unable to verify software update." UserInfo={NSUnderlyingError=0x600001b80270 {Error Domain=OSPErrorDomain Code=302 "The signed AP ticket could not be found." UserInfo={NSLocalizedDescription=The signed AP ticket could not be found.}}, NSLocalizedRecoverySuggestion=You can try again to complete the installation., NSLocalizedDescription=Unable to verify software update.}
2019-06-01 11:07:48-04 MacBook-Pro Installer[4173]: ManualAdoption: stashToken is Nil, softwareupdated did not authorize a token, stashing has failed!