You can't remove components from an installed package, and uninstalling the package will remove all the components. If you insist on getting rid of the package, the process you'll need to go through may range from a mild irritant to completely obnoxious. You may want to just deal with the package existing until you decide to move to to a new org or can dedicate the time you need to fix this.
The process to fix this would be as follows:
First, download the package. Unmanaged packages don't hide their content, do doing this is trivial. For my solution, I recommend Salesforce DX, because we'll be using it for this process.
Second, create an Unlocked Package with the contents you just downloaded. You'll use this to restore the miss configuration when you're done. Make sure you test this out installing the package in a spare org to make sure it works.
Third, back up any objects and fields that will be deleted. Give your users warning not to use those objects and fields until you're done, because that data is going bye-bye. You can use the "retain data" option while uninstalling, but you want your own copy too--just in case.
Fourth, uninstall the package. This step may be complicated if you have dependencies you need to untangle. I suggest adding those dependencies to the Unlocked Package, as you'll need to restore those later. Repeat the package version/deletion cycle until you successfully uninstall the package.
Fifth, install the Unlocked Package. This should put all the metadata back in place for you. Further, you'll be able to use this package to migrate to new orgs in the future, etc, or even just use it as your primary development life cycle going forward. This new package type even allows uninstalling without deletion and automatically merging into existing unmanaged metadata.
Sixth, reload any missing data that you had backed up. If you've gotten this far, it should be pretty trivial from this point.
