I'm trying to make a wireless charger. But I want to make the distance farther. So, How can I increase the distance of wireless power transfer? Does making the frequency higher will increase the distance? Or winding more turns in the coil? Or making the voltage higher?
Beyond a certain distance magnetic flux density reduces with the cube of distance. To avoid this you need bigger diameter coils. Try googling for the formula because unfortunately I'm on an android and haven't learnt to embed pictures using one.
Something also to consider is making a passive coil extender if this is practical for your application. Basically it's two sets of coils that take power at the drive end and deliver it to the receiving end.
Lowering inductance will cause a higher coil current and this delivers more flux at a greater distance for a certain drive voltage but you will need to consider litz wire to make this effective. Basically you need to maintain Q at lower inductance values.
increasing the power will have a small effect on range, but as wireless power is near-field signal strength will fall off rapidly as you increase distance.
So, larger (diameter) coils is the only practical way to increase range.
Your range is pretty much limited to one coil diameter. You can stretch this a little by increasing the Q of your coils, and backing/coring them with ferrite.
Increase the Q by using Litz wire, and high Q caps.