Tapering from Mirtazapine to Citalopram any advice please?

Im tapering from Mirtazapine 15 to 20 citalopram im just abit nervous about what to expect so had anyone done this and what can i expect any advice would be much appreciated . thanks

they have said to take 15mg mirtazapine one night then the next day take a citalopram had anyone done this before?