Why? If you are doing it to make the file smaller, you probably will be disappointed.
If you want to do that for another reason, such to neaten up, there is a procedure.
Money has operation called Archive. For most users, it does not do what
they wish it did. So for them, the advice is don't do it. Those who
are looking to make the file appreciably smaller are usually disappointed.
Archive makes a copy of the file being archived, and gives it a name
with Archive added. You provide a date to Money when you archive, and
Money removes non-investment transactions that have earlier dates. It
adjusts the account Opening Balance to compensate for the removed transactions.
There is no way to fully re-integrate the older transactions with the newer
ones. There is an incomplete way that takes some effort. For most, the best
thing is to generate reports that cover the date range of interest, but to
keep all of the data present.
Now you may be the person who will want to Archive despite the potential disadvantages.
To Archive, click File->Archive, and follow the directions.