It depends if the orginal cables can be connected without the use of a junction box. If so, you simple connect the the cables on to the right terminals. So your orginal in-coming Live is connected to live on first light then connect from there to live on second light fitting and returning the neutrals by connecting the same way but acroos the neutral side. Most of these types of lights are now double insulated and there is no need to earth but check the manufactures instruction. You may still need to earth.
Please be aware that some domestic installation do hve to comply to Part P of Building Regs. The Doctors has info in the projects part of this website.
Good Luck and be safe.
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