you can add these params to srcds startup:
-autoupdate -steam_dir steamcmd -steamcmd_script update.txt
create an "update.txt" file inside steamcmd folder with the following content:
// update.txt
//
@ShutdownOnFailedCommand 1 //set to 0 if updating multiple servers at once
@NoPromptForPassword 1
login anonymous
force_install_dir ../
app_update 740
quit