Easiest way is to give them a call. Guaranteed increase. Don't wait and sell to your limits. Whatever you are comfortable with though. If there's live chat available on your account then you can use that too.
Contacting eBay doesn't guarantee an increase, if they have grounds to, they can refuse your request.
But if your desperate for higher limits, and you've tried selling to your limits, then giving a call would be a good idea, and you'll have better success then as they can see you're utilising your existing limits.
how to increase selling limits ebay! 
They can be quite helpful sometimes.
