How can I remove black timer buttons?

I have a rangemaster Tecnik 110cm gas range cooker. We are replacing the fascia but are unsure how to take off the six black timer buttons under the clock? The large knobs just pull off but the little black buttons won't budge. You must be able to replace them as they are advertised as spare parts. Can anyone help as an engineer starts at over £115 and budget won't allow!