With only 5GBs of free space on your mac you are running the risk of your mac locking up and becoming unusable.
The download may only be 1.42GBs in size but this is a compressed file and once uncompressed and ready to be installed
will be at least twice the size.
Generally macs need at least 15-20GBS of free space to function normally, there are numerous background tasks the mac is constantly doing and it needs free space in order to this housekeeping.
Copy files you do not need on a daily basis to an external drive, Movies, Images and Music often take up the most room.
Having copied the files over confirm they have copied over successfully then you can delete them from your mac.
Restart your mac.
Then install the update.
Always try to keep a minimum of 20GBs free, more would be better.