How can you selectively dispel spell?

Suppose an enemy have blur and slow cast on them.

Can I use dispel magic to end the magical effect blur, without dispelling slow?

The above spells are just examples. This question mainly ask about how dispel magic can be used to end one spell affecting a creature without dispelling other spells.

What are the conditions must be satisfied to do this? Does the will-be-dispelled spell must have a perceivable effect to be able to be targetted? Does the spell must be lower than dispel magic? Must I name the spell I wish to end? Must I name the effect (“whatever making him looks blurry”)?