The last week of next month ubuntu will most likely release 18.04 LTS. Now my system is 14.04 and next month I want to upgrade it to 18.04. Can I directly upgrade my system from 14.04 to 18.04 or I have to first upgrade from 14.04 to 16.04 and then to 18.04? I really want to avoid the second method of upgrading.
Edit:
How should I update 14.04 to 16.04. I tried this method sudo update-manager -d and installed all the necessary software and restarted the system. Again I run sudo update-manager -d and it showed that my computer is upto date but doesnt have any button to update to 16.04
No.
Ubuntu does have LTS→LTS upgrades, allowing you to skip intermediate non-LTS releases...
But you can't skip intermediate LTS releases. You have to go via 16.04.
Unless you want to do a fresh install of 18.04 on release.
I should also note that the LTS upgrade pathways are usually only available some time after the main release. So don't expect to be able to upgrade from 16.04 on the day of 18.04's release.