up the 2:nd string a whole step to C#, compare with the 4:th fret on the 5:th
up the 3:rd string a whole step to A, compare with the 5:th A.
up the 4:th string a whole step to E, compare with the 1:st and 6:th strings E.
Open A-tuning is the same as G-tuning only that it is tuned a whole step higher.
On an electric guitar with very thin strings and low action it makes it easier
to play with a slide or bottleneck if you tune up. I will not recommend this on
an acoustic unless you have ultra thin strings on it. The risk is that the neck
and top canīt take the much higher string tension. Check also and playing
in open G and A.