My dr wants to switch me from 20 mg of lisinopril to 50 of Losartan will the transition be easy & should I worry more about potassium on losartan?

It's OK to switch. Lisinopril and Losartan are both great medications with equal efficacy and you can easily switch from one to the other. They both may increase the potassium level equally but unless you have advanced kidney disease, neither should affect your potassium significantly.