If your internet is slow, then simply talk to your ISP (internet service provider) about getting faster internet.
If your computer is slow, but fairly new (2-3 years), or was a high end machine as much as 5 years ago, then consider some upgrades
-SSD to replace your hard drive. This is the single largest speed increase you can get for any PC
-4 to 8GB of Ram will help if you have a lot of software running
-If on a white-box (home made computer) then consider getting a faster processor. Black-boxes (prebuilt machines like Dell or HP) tend not to let you upgrade such things easily.
-Try uninstalling junkware, and make sure you do not have any viruses or adware. Uninstall any toolbars, run malwarebytes to make sure you are not infected
If your computer is older than 5 years then it may be time to simply buy a newer machine as there are no major upgrades that you could do to overcome the bottlenecks of your CPU and buss speeds.