The first thing to do is remove your watch and place it face down on a folded cloth or towel. Make sure it is on something that will protect the face of your watch and not scratch the glass. Then place this cloth onto a flat surface, such as a table or countertop. Once you have got the watch face down, look closely at the area where the watch band connects to the watch itself. The vast majority of watch bands are connected by a spring bar, which passes through a loop or hole in the band and fits into indents on the shoulders of the watch.  The spring bar is a small metal bar that can be depressed at each end, like a spring. When pressure is released the bar extends at each end. When fully extended the bar will snap into place in the shoulders or lugs of the watch and hold your strap in place. To remove the band you need to detach the spring bar. You can do this with a specific tool, known as a spring bar tool. If you don't have this tool, you may be able to remove it using a small flat head screwdriver, or something similar. You may also be to remove it without any tools, just by using your hands, but this will be trickier.  If you have a spring bar tool, insert the pronged fork end between the band and where it connects with the watch shoulders. You can press the bar in from either end. Then gently apply pressure on the tool, pushing lightly away from the watch. This should push the spring bar down and release the band.  You can replicate this with another small tool that fits in the same space, but be careful not to scratch your watch or damage the band. If you don't have a tool, you can try using a paperclip to compress one end of the spring bar, and then carefully lever out the band. Once you have detached the band from the watch, slide the spring bar out of the loop in the band and put it to one side. Do this for each half of the band. You may need these bars to attach the new band, so it's important that you don't lose them.

TL;DR in Indonesian:
Letakkan jam tangan menghadap ke bawah. Temukan bilah pegas (spring bar). Lepaskan bilah pegas. Keluarkan bilah pegas dari tali jam.