How to unblock roblox.com

Try with Ultrasurf
Ultrasurf is an application which enables you to browse blocked websites freely. As a lightweight application Ultrasurf is compatible with all configurations and super simple to use
Ultrasurf can help you bypass the internet censorship, create fake IP to pass the firewall to access the blocked websites. Through this program, you can also access such websites that the internet providers in your country block.

The process of unblocking depends upon how was the block imposed on you by the specific website. If the specific website has blocked your user name, you can create a new account with some other user name and start accessing it. If the website has blocked your based on your IP address, you can either use a VPN service or make a request to your Internet Service Provider for an IP address change. Then you can access the website. Once you have enabled a VPN service, you can visit IP-Details.com and have an IP lookup to ensure the change in your IP address.

If someone has blocked you from accessing the domain roblox.com you can try a couple things. Try accessing the secure version of the site:
https://www.roblox.com/Landing/Animated

If that doesn't work, try using a proxy service. This will work unless your administrator has blocked access to the proxy service:

https://proxy.org/