Let's talk about some of main reasons.

1. There is no need for tuning.

Acoustic pianos have to be tuned once or twice a year. However, since sounds of digital pianos are in digital format, they never go out of tune. Forget about paying a tuner all time and save.

2. They are portable.

A regular upright piano could weigh over 500 lbs. A grand piano weighs a lot more. Compare this to digital pianos that weigh less than 100 lbs. You could easily carry one under your arm from gig to gig. Transportation is easy. The fact that many of them could be disassembled is also a great advantage.

3. They cost much less.

Acoustic pianos are very expensive and out of price range of most people. You can save yourself a lot of money by buying a digital piano. For less than $2000, you can get one that is top of line. You will even find those that cost only a few hundred dollars.

4. You don't have to disturb neighbors.

Worried about disturbing neighbors? There is no need to be worried. Simply plug in a pair of headphones and play silently. With an acoustic piano, it's obvious that you do not have that privilege.

Tools.

You will need a small needle nose pliers to cut and bend strings, and a string winder to help you wind strings quickly.

Remove string.

You should change each guitar string one at a time. That way, you will avoid warping guitar neck, and you will be able to quickly tune new string to other strings.

I usually remove 6th string first. Use your string winder and turn tuning peg until string becomes very slack. Now cut off twisted end of old string so that it slips easily out of guitar. Then wind top section of your string out of tuning peg.

What you do next will vary depending on type of electric guitar you have. The one I'm using, strings go through body. Remove old string. Pay close attention to way your old string comes off, and do opposite when putting a new one back on.

Replace string.