What will happen to my server if i resize?
Im planning to resize my Linode server but my script needs to be running 24/7, if i upgrade my server, will the script/OS stop to reboot?
You can resize your server anytime but the resize won't take effect until you reboot (until you reboot, you'll be paying for the larger configuration while only getting the service of the smaller one).
Alternatively, you can allocate a new server of the appropriate size and move your services/apps to the new server. When that's complete, and the new server has taken over from the old one, you can shut down & delete the old one.
Both solutions will require a few minutes of downtime. Of the two, the first is less work and will require less downtime (been there, done that…on both).
As always, backups are your friend.
P.S. 100% uptime is a pipe dream…always has been; always will be. No reputable service provider (at least any that have lawyers that, you know, actually graduated from law school) would make that promise!