Only the far-end equipment of your ISP sees MAC.
Is "megaupload" an ISP "sales phrase", or a website?
If a website, changing MAC does nothing.
So you're actually tying to force your ISP to issue new IPs to you?
IPv6 or IPv4?
(You don't have to change MAC to get a new IP address for IPv6)
(and doing that via IPv4 without ending the lease may cause other issues with your ISP - that they'll eventually trace to you, and not like!)
also, if it's a website - @psherman notifying a mod, because asking how to violate terms-of-services, etc. is not allowed on this forum