How to Splice Rope
Knots significantly decrease a ropes strength. Ropes are designed so the strength comes from an equal amount of pressure on all the strands of the line. When you tie a knot your putting an uneven load on the rope. In some cases a knot will reduce the breaking strength by 45% while an eye splice on the same line retains 95% of the strength of the line.
There are many kinds of splices for different types of rope. Some of the most common are listed here.
Most of the major ropes companies provide video's on how to splice their line. In google type the name of the rope you have and the word splice and that should bring up a video on how to splice that line.