I have a couple of ideas.
Stick with your old plan, but replace some of it with a piece of the new plan. Said another way, ease into it bit by bit.
Break the new routine into several parts: A,B,C. Do part A one day, part B the next day, part C the next. Repeat for a couple of weeks until you are sure of yourself and your new routine.
Alternate. One day do your old routine, next day do your new routine. Variety in exercise regimens helps keep the metabolism revved up.
Ask yourself why you wanted a change? The old plan wasn't working!
I change things up from time to time and find that it helps keep me interested.
"The only way to hurt your body is to not use it." Jack LaLanne
| current weight: 139.4