This can be a problem with user permission rights of the webserver / php stack.
If you e.g uploaded the limesuvrey via ftp the files were created with certain user rights. It might be possible that limesurvey is running under a different user / permission set and cannot replace the file under "/locale/am/LC_MESSAGES/am.mo" on its own.
1.) If you are currently running surveys in your installation I wouldn't do the update till you talked to your administrator.
2.) If you are not running any productive surveys at the moment, try to do the upgrade. If you cannot finish it, note error messages and send them to your administrator.
3.) You could update the manual way like you install limesurvey the first way.
To really find out, what the problem is more information is needed.
PHPInfo, Webserver Apache? You might find an error log file generated by php in your webspace. You can also look into the apache logfiles to get a clue what might be the cause of these problem.