I'm currently using ngx-admin which is on version 2.3.0 and now it is updated to 3.0.0 see here. I just want to know how to update it without affecting my entire project.
By looking at your tags, I presume your app is running on Angular 6 where as if you read the CHANGELOG.md link which you've mentioned in your post, it clearly states that,
Angular 7+ now required.
The following libraries were updated:
@agm/core
@ng-bootstrap/ng-bootstrap
@swimlane/ngx-charts
ng2-ckeditor
ngx-echarts
Hence I'm afraid you will have to upgrade your project to Angular 7 in order to execute it seamlessly.