I have learning guitar for about 2 months now and I learned my chords at the same time concentrating with my fingerstyle. I'm quite good at fingerstyle now even when changing notes. But I found it challenging to change chords and strumming at the same time though I know the chords well. Can you guys give me some tips
A bit more detail following piiperi's good suggestion.
First play a good clean chord. Try to have at least some fingers touching others. Then release pressure, but still keep fingers touching the strings. press down again, and strum, to check the sound is still clean. Do this with each chord several times.
Next, play a chord, but this time, take your fingers off about a couple of millimetres, just not touching. Then perform the hammer-on, ensuring that all fingers go down with some force, and importantly, at the same time, together. It's no good making a chord in instalments! It all needs to be together. Obviously, any open strings are not going to sound while doing this, that's not important. But when you do hammer-on, listen to hear the notes that you did press down. They must be clear, not muffled or rattling. just to make sure, strum the chord as well.
When you get better at this, then's the time to raise your fingers about 10mm off the 'board, and hammer-on from there. Look all the time, and after a lot of attempts, try it without looking. Then, hammer-on between two chords, say E and A. True, there may only be three notes to hear, but that's no big deal.
Last stage is to play a sequence slowly, but in time, and tidy up all the chords and changes. Working towards playing at the tempo required. And remember, your fretting fingers shouldn't hold up the timing of your strumming. That's something else to be aware of - if you hold back the strumming to get the chord shape right, you're actually practising that delay, which will stick with you. Not good !
Practice the instantaneous pressing-down of the chord shape with your left hand fingers, without doing anything with your right hand. The pressing-down of strings makes a "hammer-on" sort of sound. It can't be as loud as fingering normally with your right hand, but try to make it reasonably loud, or at least loud enough to hear each of the fingered strings sounding. Focus on getting the sound to be rhythmically precise and in time, not an inaccurate mush of sound. Try to "comp" with just your left hand, a steady accurate rhythm, for example one pressing-down per beat. One-two-three-four, ... Imagine being a single-armed guitarist who has to accompany the song.
This left-hand comping exercise should force your left hand to get in position slightly in advance of the rhythm, so each fingering/shape/grip is fully done and ready when it's time to play it.
If you know the chords well that is a plus. When changing chords during strumming, quickly lift all your fingers simultaneously off the strings of the first chord and with the shape of the next chord in your head try and make your fingers change to the new shape all at once and land simultaneously on the next chord. The idea is to make it one consolidated motion as opposed to moving one finger at a time.
Imagine the strings are railways and the fingers are the wheels of a train. You can't displace one wheel after the other. The whole wagon has to be moved at once. *1)
Start with Am and E changing tonic and dominant (pattern 123)
or C - G7 only changing the index (1) and the Bass (C-G) then play the full chord 123 and turn softly the wrist diagonally that the index is on string 1 and the 2,3, are move to string 5,6 in one movement.
Analog you change G and D7: 1,2 move from string 5,6 to 2,3 and the ring finger moves from fret III to II.
When you play barré chords you can transfer this method 1:1
A good practice is to play the final of A day in the life (Sgt. Pepper - Beatles):
*1) Play the E-C-chord and move the fingers 123 (mind the train) sliding from fret to fret, keep the the rhythm of the r.h. let the open strings E,b,h sound.
When starting barré chords do the same with fingers 234, then add the index for the barré.