After you’ve installed Ubuntu, you may want to tweak your system further, such as improving how Ubuntu connects to the Internet, and therefore speed up your web surfing.
To accomplish this, we’re going to configure IPv6 and the TCP Window Size. Please remember to back up any critical files or data you may need as well as keep records of the settings you change. Doing so will help you recover in the event of a disaster. Keep in mind that you perform these configuration “tweaks” at your own risk.
These configuration tweaks are completed by entering commands into your “Terminal”. We will use Gedit although you can use Vi, nano, etc.
As a side note, if you do not want to enter “sudo” for each command, just begining your terminal session with this command:

sudo su

IPV6 is an Internet protocol. Currently most applications use IPV4 and this can cause conflicts which slow down your system.
Complete the following to disable it.

sudo gedit /etc/modprobe.d/bad_list

and type this in:

alias net-pf-10 off

Then save the file.

Speed up Broadband Internet by editing the appropriate configuration file and adding the following information. – Or, you can use a tool called PowerTweak from here: sourceforge.net/projects/powertweak

sudo gedit /etc/sysctl.conf

The first four line deal with window size and you need to enter numbers that are best for you (because these ones may be too high). Here is what I mean by this:
Computers communicate by sending packets of data back and forth. When they connect with each other to send these packets they use the TCP (Transmission Control Protocol).

Your computer could begin the connection with a small package size, then the other computer might respond with a larger one. In turn your computer will reduce (scale down) the size of the package (to a bit more that your original package size). The other computer again responds with a larger packet size. This cycle continues until your computer or the responding computer meets their maximum package size.

If you choose a windows packet size that is too big, you will notice slower broadband performance (524288 works for me). If you notice a slow down, then reduce your window size.
The largest size you can use is 65536, however these are the three settings that seem to work best:

524288
262144
131072
Which are all multiples of 1024 (or 1K).
Now add the following to the end of the file:

net.core.rmem_default = 524288
net.core.rmem_max = 524288
net.core.wmem_default = 524288
net.core.wmem_max = 524288
net.ipv4.tcp_wmem = 4096 87380 524288
net.ipv4.tcp_rmem = 4096 87380 524288
net.ipv4.tcp_mem = 524288 524288 524288
net.ipv4.tcp_rfc1337 = 1
net.ipv4.ip_no_pmtu_disc = 0
net.ipv4.tcp_sack = 1
net.ipv4.tcp_fack = 1
net.ipv4.tcp_window_scaling = 1
net.ipv4.tcp_timestamps = 1
net.ipv4.tcp_ecn = 0
net.ipv4.route.flush = 1

After adding these line you do not need to reboot, instead just reset the file by issuing this command:

sudo sysctl -p

After completing this, you should notice improved web surfing speed. If not, remember to go back and adjust your TCP window size and try again.

Part 2 of this article, which contains more technical information, can be found here: ubuntulinuxhelp.com/speed-up-your-internet-connection-in-ubuntu-linux-part-2/