The old Led strips may have been heavily glued or sealed.
Simply remove it by forced without damaging the thread and sole.
Then upon replacing the new strip, you may use glue to stick the cabel properly at desired area. wait for the glue to dry first before inserting the insole.
Please take note that for larger size (Size 26-30), the length of the strip may not cover from bottom to top of the shoe.
It will be slightly shorter. Simply arrange the LED to its full extent.
It will not much affect the light output.