How we can safetly switch from the combo (100 mg ZOLOFT + 150 mg WELLBUTRIN (bupropion) XL) daily to the combo (50 mg ZOLOFT + 300 mg WELLBUTRIN (bupropion) XL) daily?

Who are 'We'? Is one of the 'We' your Dr? If not - it should be. And then, your Dr is the one to take responsibility for this transition. Psych meds are not a good DIY project. Find professional guidance. Best!