Recording a grand piano is plain hard. Recording a vertical piano is downright a pain in the #$% and rarely will sound great. First you need to get the thing tuned and not by a hack. It would also be a good idea to have it regulated. As to the recording itself, here are some general tips for you.

1-Move the piano away from the wall and at least a third of the way into the room. Don't put it in the exact middle.

2-Lift the top and remove the knee board. Also, if the music is memorized then remove the front board where the music rack is.

3-You are going to have to experiment lots with mic positions. A pair of NT55's would be a good pair to start with. I would try the A-B stereo mic technique from about six feet back. Another alternative would be one mic on the left side pointing at the bass hammers and one on the right side pointing towards the treble strut. Another place to try is 1/3 in from each side at the back (where the soundboard actually is). These are just starting places. There is no way to actually predict anything without seeing your room etc.

I don't think I've ever heard an upright piano ever sound like a grand no matter how nice it was. Be it Steinway, Yamaha, Baldwin, etc.. They all sound like uprights. Sure, you can get close. You can get far. But to get them sounding more like a grand and you need near and far. I would consider using 5 microphones to do the job where only 2 might be required on a grand. 2 over-the-top opening. 2XY in the room. One down low in the back near the floor. A little reverb and you might get there. But then with the money you might spend on equipment? It might be cheaper to purchase a grand?

Yamaha C-3
Mx. Remy Ann David

All that's been said here is valid but I would add a couple of things.
The sound of a piano, like any other acoustic instrument, is very much in the hands of the player. If the player has a good recording technique and makes the piano sound good in the room then recording it suddenly becomes very much easier for the engineer.
For me the fewer mics the better. I often use a stereo pair about three or four feet away from the back of the piano and aimed at about halfway up the height. I've used Shure SM81s to good effect and also AKG C414s in a coincident pair.
Some filtering of the low mids can be a good move but we're talking subtle here and is very much dependent on what you're hearing on the day.
Lastly..tuning. The point has already been made here but I have to tell you that all piano tuners (the human ones) are not equal. I've used four different guys over the last 20 years depending on availability and only one of them makes our studio piano sound brilliant. The other three just tune it and it makes a hell of a difference! One bloke turned up and used a Korg electonic tuner!
Something to think about. :D

open the cover ,and then FIX A mic in

Several of these comments will be repeats and some won't.
1. Is the piano going to be used as just part of an ensemble (for example a rock ensemble)? If so you may pull off it sounding like a grand. And if it doesn't sound like a grand, it may sound cool in its own way in this context anyway. If not, there is no chance it's going to sound like a grand.
2. there are many other ways it could sound itneresting: burying it at the bottom of a well kind of spooky effect (if the piece is slow, that kind of thing).
3. If your room doesn't sound terrible, you could move the mics way out into the room to keep the sounds of the hammers from sounding so prominent.
4. it does have to be perfectly tuned. and as mentioned above, tuners vary dramatically.