What version are you trying to upgrade, you can only use the upgrade wizard on versions prior to 8 (I think).
If you’re doing it on 7 or earlier, could be the upgrade cache is corrupted. You can delete it and start over.
remove/rename:
in the \cache\upgrades\temp\ folder - remove/rename upgrade_progress.php
If it’s failing because it’s timing out (another common issue). You can increase your max execution time in php.ini
It could also be because you have a large cache or upload folder and it just takes forever to go through all the files. You can skip folders in the check by:
modules/UpgradeWizard/systemCheck.php Find the line in the file that initializes the $skipDirs array and add the two folders it mentions in the comment ‘cache’, and ‘upload’, to the array initialization.
add directories here that should be skipped when doing file permissions checks (cache/upload is the nasty one)
$skipDirs = array(
$sugar_config ['upload_dir'],
'.well-known',
'.svn',
'.git',
'cache',
'upload',
);