Its damn big hassle. I changed one and really many things you have to do.

For a start, banking details, like TAC and etc.

Next you have to change all the numbers in your online account, like those shopping (shopee, amazon), food delivery (foodpanda), insurance, job application websites, service site (like jpj, mysikap, tnb, water) and hell of a lot more.

Some you cant even change without receiving some PIN on your old number. So my suggestion is to keep your old number for at least a month of 2 to ease the process.

Damn, its really troublesome for ppl like me who did always everything online. Like a nightmare.