Well, the first thing I would suggest is to harden your kernel (see the blog post I referenced above).
That, though, is not meant to block big SYN floods. If that hardening doesn't stop the flood (and I suspect it might not), you'll have to look to another option:
1. Rent a hardware firewall
2. Have someone knowledgeable set up a proxy service like CloudFlare (it must be someone knowledgeable)
3. Talk to your host about blocking it at the network edge (you may have to pay more for this help)
I don't doubt that you're with a good host, but not all hosts specialize in DDoS protection. You may need to pay extra to your current host to get more help (or rent hardware) or find someone who can help you set things up (or switch to a host that specializes in DDoS protection). Either way, our Anti-DDoS Proxy service isn't right for you and changing settings in LSWS isn't going to affect things.
The last option, of course, is just to wait for the attack to end. I assume that's not an option, though.
m