We created a managed package in our developer org and made it a released package. Afterwards, we decided to remove some custom fields from the managed package but saw no way of doing this in the org.
After looking at the documentation (e.g. here), I discovered that I need to ask Salesforce to enable the feature for us to be able to remove components from a managed package.
Once this was done, I expected an option to remove the component from the managed package in package manager. This was not there, however, so it wasn't clear how to actually remove the component from the managed package. The documentation isn't really clear on this either.