Hello @danmassa7
I’ll try to make this easy for ya 
First of all The latest package is Graylog-4.2.7, If this is what you want then the following will work for ya.
NOTE: Make sure you have backups of your configuration file.
So, what I’ll try to do is sum it up on how to upgrade Graylog.
Here are the steps I execute in order.
1.Before Upgrading make sure your system is fully updated, try not to use the Y flag incase you see a package updating that may affect you system (i.e. Elasticsearch, MongoDb, etc…)
NOTE: Check to insure Elasticsearch/MongoDb packages Do Not exceed the requirements
yum update
2.Stop graylog service before you upgrade.
systemctl stop graylog-server
3.Install new Graylog 4.2 package.
rpm -Uvh https://packages.graylog2.org/repo/packages/graylog-4.2-repository_latest.rpm
4.Make sure your repository cache is clean from Old version of Graylog.
yum clean all
5.Perform Graylog upgrade
yum upgrade graylog-server
6.If upgrade command doesn’t work you can use the following also.
yum install graylog-server
NOTE: At this point make SURE you have the correct Graylog Configuration file (server.conf) , some settings have changed in the newer versions. To insure you have the correct server.conf there should be a file called server.conf.rpmnew in the Graylog directory ( /etc/graylog/).
7.This may not pertain to you but I though I would Highlight it incase. Check the permission on Graylog directories.
ls -al /etc/graylog
8.Once everything is done I started Graylog service
systemctl start graylog-server
9.Now TAIL Graylog file and look for errors, warnings, etc… Sometimes the error’s are not at the end of the log file.
tail -f /var/log/graylog-server/server.log
10.Last step 
Make sure you refresh you browser and you should be done.