The web is abound with theories of uncapping cable internet to increase speed…. but is this true??
If your ISP is throttling your connection, you can't do much. I would advise you to switch ISP's as soon as possible though, as no self respecting provider would throttle their users to anything lower than what they paid for.
You can test to see if your connection is being throttled using M-Lab's Glasnost test, which is a free web service. Test your upload/download speed using speedtest.net, if it's significantly lower than what you're paying for consider switching providers. (Uploading/downloading in background processes will obfuscate results)
The question is whether the speed cap is technical or logical.
If you pay for a 16Mbit connection there is no way you can hack your connection to be e.g. 20Mbit simply because your account/line is locked to that maximum speed by your Internet Service Provider.
If you pay for a 8Mbit A/S-DSL connection but only get e.g. 4Mbit it is mostly because of technical circumstances in which case you may be able to do (a little) something. Basically your connection is throttled because your lines noise margin or attenuation is to high to support the higher bandwidth ~ it would cause your modem to lose synchronization with the DSLAM and drop the internet connection every now and then (sometimes every few seconds).
Some of the basic things you can do is not to have both your modem and it's cables right next to a power outlet or cable. Also shortening the distance between the local loop (buildings main outlet) to the first telephone outlet and the modem might help.
More advanced techniques include ferrit magnets and other stuff but it's questionable if it really helps.
In most cases the only way to get better speed is to try to switch the line to the DSLAM or using a 4-wire instead of 2-wire connection ~ both require actions from your Service Provider. Switching to a 4-wire connection may also require a switch of your modem and for private connections you mostly have to pay an additional fee for using the additional wires.
I believe this is a myth that's been going around. The only way to "uncap" your Internet connection is to pay your ISP more money.
There are some instructions out there about how to "uncap" and it's anyone's guess as to if they work. But even if they do, you'd be violating your agreement with your ISP, and they'll likely seek additional money from you or terminate your service if you are caught.