Manual states SUZUKI ATF 3317
Normally if it's just 3-4L change that means what you're doing is just to drain the fluids from the drain sump. The balance of which in the torque converter can only be extracted via a machine.
For my 1.8L Optra it takes in 14.2L of ATF for a complete flush and refill, for a SS, a figure of 10L would be realistic for a change.
If you go for Option one for someone with a tight budget, replacing it gradualy at 20K interval is better, but if you go for a full flush do remember that if you had not done one and regularly and only intend to do so pass 100K KM please do not!!! Chances of GB failure is higher since there's more debris in there and the seals may be damaged due to the extra pressure required to pump it out.
Trust me a flush is always better than a replacement but don't do it when it is too long overdue. Once a full flush is done if you're on synthetics a 60-80K interval is a safe bet.
Do not mix different brand of gear oil together as the diffrent performance and visco will damage the GB in the long run.