Roblox is an online game platform created by David Baszucki and Erik Cassel in 2004. The platform is mainly for young people to play games and socialize.For users to use it, they have to create an account with a profile.

Seems that if you want to delete a Roblox account for any reason it can only be done on their side. You have to contact Roblox customer care to do it for you.

You can call them by this number  888-858-BLOX and request an account deletion. Of course they will want to verify you, so you will need to have your email, name and address ready.

You can also write then an email to them and ask them to delete your account. Contact them through info@roblox.com. You will have to include the reason for account deletion, your account email, full name, phone number and address for identification verification.

The other way to do away with roblox account is to ignore it and let it idle for a full year without logging in. After a year, ROBLOX will delete all accounts that have been inactive. Your personal information, such as name, phone number, email address and location will be deleted from their servers.

See here how you can delete an Eclipse account.