Start of course by cleaning the bottle.

• If it is a water bottle nothing to do. 
• if is a soda one, then rince it to remove sugar.

Remove most of the stickers. The remaining glue will be suppressed after.

Although it can be considered as optionnal I do start by putting some pressure into the bottle. I have adapted a tyre valve to a bottle cap and use it to connect to a compressor. No need to put a lot of pressure !

Then you should use a hot gun to start to warm the bottle so that any "carving" will be progressively removed and you get an almost cylindrical bottle !

After what, the pressure still there, you can finish the cleaning stage. Pressure helps a lot, you can push on the bottle without deformation. Use solvant to remove strong glues or water and soap if enough.

Then insert a cutter blade at the very bottom of the bottle where you usually can see a "line". Once again pressure helps to enter the cutter !

Then with scissors simply cut le whole bottom, progressively shifting the cut to the right (if right handed) so that a primer of the ribbon is visible (will help to cut the ribbon !)