Measure the length of the space that you need to fill. Vinyl fence manufacturers will recommend using a preassembled gate section, if one will fit, before cutting a section down to size. Use this measurement to determine the amount you will need to cut.
Stabilize the panel on a table and place the area that you are about to cut off of the edge of the table. Make sure that you are cutting between the vertical pickets and not through the vertical pickets. For vinyl fences that have the rails built into the pickets, make sure that you leave enough exposed rail on each side so that it can connect to the posts. For vinyl fences that have a slot where a rail will slide in, this is not an issue.
Cut through the fence with a circular saw. If you want to keep an end design on a lattice-topped fence, only make one cut. If you don't care about the end design, make two cuts to remove both ends. If your vinyl fence has separate rails, make sure to cut those as well. The rails may be a few inches longer than the panels, so keep the proportions that were in place before you started cutting.
Complete the end of the lattice top by cutting a piece of excess picket equal to the length that the lattice end needs to be. Cut this board down the side so that it can open up like a book. Wrap the board around the end of the lattice and secure the end with white silicone cement.
Notch the end of any rails that require it. Some vinyl fence rails need notches to stay connected to the posts. Insert the side of the rail that you need to notch into the jaws of the notcher and press down on the handles. You should now be able to install the panel according to your specific fence instructions.