Are you kidding me? Don't you know how your own hosting works?
I've just created a new site, called letmeshowyouhowitworks.wowlaunch.com
So, I get in as an admin, and under Site Section > Site Urls I see this writing:
"Full Domains are available to subscription sites. Upgrade today to receive all premium features."
If I click on "Upgrade", a new window appear. There, I can chose a plan with a subscroption fee (Essential, Premium or Ultimate).
Included in all those plans, there is a "Full Domain Support".
So, if I click on PAY, it's YOU that are giving me my "full domain site" called letmeshowyouhowitworks.com. I'm not gonna register anything anywhere else! No GoDaddy, no Aruba, nothing...
That's exactly what I did two years ago for gildasorellanza.com
So, stop saying that I purchased my domain somewhere else, I didn't do anything at all!
What they mean by "full domain support" is that they support those who wish to use their own domain names to point to their sites.
Having looked up your domain name, the details of who owns it (I believe) are here: https://www.whois.com/whois/gildasorellanza.com
I'd suggest you work out who that person is (a guild member/ex-guild member, perhaps?) and contact them.
Gamerlaunch do not provide domain names other than those with their own suffixes on. They provide *support* if you have your own domain name. They even provide suggestions of where to get your own domain names. If Gamerlaunch sold domain names, they would not go around advertising others.
As far as how to change the A Record .. it varies from domain name provider to provider. I use a company called 1and1, which doesn't have the same way of changing it, but once you know the IP address it is now, and roughly where to look - mine is under "changing dns settings", etc.