Upgrading to 184.108.40.206 will be easy as it is only bug fixes + security fixes.
BTW: It is highly recommended to update to last 1.8 for security reason (see the home page of this site)
1.8.5 will be released pretty soon. Damian?
To upgrade to 1.9, when it will be stable , it depends how many files you touched. Did you change a lot of templates, a lot of code? But if you added only css, it will not be too hard