Question: Q: Mac

If you simply want to update the OS you can go into the Mac App Store and press on Updates.

if you need a new Mac you need to buy it and you’ll be guided through transferring your data by the new machine.

This is a great guide that covers the upgrade

https://www.apple.com/macos/how-to-upgrade/

Upgrade what? The system? The memory? The hard drive?

Please read the following user tip and restate your question/problem in detail: Writing an Effective Apple Support Communities Question - Apple Community    

What iMac do you have?

https://support.apple.com/en-us/HT201634

What do you want to upgrade?

The software and/or the hardware?