I am a total beginner at piano sight reading. I find it difficult to change chords or move from one octave to another while looking at the sheet without pressing the wrong notes. Any advice?? thanks.
Apart from years of practice, which will bring this sort of ability out naturally (eventually), there are a few things you can do in order to help the process along:
One is learning to play scales while blindfolded or in the dark, so that you cannot see the keys at all. I would recommend starting with B-Major which uses all the black keys and just 2 white keys in each octave. You can start by finding the 3 black notes adjacent to each other - by touch, entirely without looking, and then finding the 2 black keys adjacent to each other (C and D sharp). then play a one octave scale blind, then move on to all the other keys.
Extend this by trying to play all the arpeggios without looking at the keys.
Try playing scales in octaves with one hand, using just fingers 1 and 5. Allow yourself to look at the keys at the start of the scale, but play the rest blind.
Take a book of pieces that you could comfortably play a year ago, and play them again while looking ONLY at the sheet music.
You might also try to develop a sort of peripheral-vision where look mostly at the sheet music but keeping aware of where your fingers are located on the keyboard.
Eventually, you will gain a kind of feel for the geography of the keyboard which makes it easier to find the jumps and leaps without taking your whole attention away from the sheet music.
Some thing else which develops over time is the ability to "read ahead" in the sheet music so that having read a few notes ahead of where you are playing, you have a split second to get a quick glance at the keys and then back to the music without falling behind.
Finally, don't get obsessed with all this, as it will happen naturally anyway. Just spend a few minutes each day trying some of the above techniques, and see if they help you - but it will still take time for improvements to show.
Learning piano or guitar or trombone or anything else involves practice. Small children use the same technique to learn to walk and talk, they just keep at it till they get it right. they stand up and fall down so many times you think they'll never get it right. but every time they stand up something is developing in their brain that helps them the next time they try. they have an interest in learning to stand, walk, and talk. That's the same process as learning anything, trying and failing is just what needs to happen till your brain gets developed to the point that it can do what you're trying to do. you may find it boring or perhaps it's enjoyable, usually dependent on your interest level. It must be said that proper technique is the way to go because poor technique is learned as effectively as good technique, but the results usually leave a lot to be desired. We're cheering for you!