how do i update my 8gb memory for larger gb amount

Do you mean RAM or Hard Drive space?

What year model and size is your iMac?

see > Identify your iMac model - Apple Support

To check if the RAM in your iMac model is upgradable.

see > Install memory in an iMac - Apple Support

Whether you can upgrade your RAM depends on the model of Mac you have. Since you have chosen not to reveal that, we can't say.

your profile shows 24" iMac with 12.3 which means you have an M1 iMac. due to the SOC construction, nothing is upgradeable where hardware is concerned.