When a firm switches systems, the instinct is to bring everything. It feels safer. In practice, moving every file you have ever touched slows the transfer and clutters the place you are trying to make clean.
Three buckets
Sort your files into three groups before you move anything.
Active records are the clients and jobs you work on now. These come with you, in full.
Reference material is what you reach for a few times a year: prior returns, signed agreements, anything that settles a question later. This comes too, because the value of switching is having it organized and close at hand.
Dormant material is what you keep only because rules say you must. This does not need to live in your daily system. A read-only archive serves it fine.
Why the sorting pays off
A new system that contains only what your firm actually uses is faster to search and easier to trust. Dragging a decade of dead weight into it on day one undoes the reason you switched.
Decide the buckets first. The move gets simpler the moment you stop treating every file as equally precious.