FAQ: Download Old Transactions

Note: 
Make a backup of your data file first.  It is always a good practice to do so when you are doing something for the first time. 
Also, for this process, record the ending balance of the account for later reference.

This applies only to Quicken for Windows.

The financial institution (FI) decides how far back to go with the initial download, usually 60-90 days.  You may be able to download more history if you go to the FI's website and download a Web Connect .QFX (not .QXF file) file.  The website may refer to it as downloading or exporting, but the idea is to get the transactions to your computer so that they can be imported.  Some FIs make you do it by month, others allow you to specify a date range, so it might take several downloads to get it all.
The browser will ask if you want to "open" or "save" the file, either will work.  If you choose "open", Quicken will start (if it is not already running) and try to process the download just like your initial download.  If you chose "save", remember where it is stored on your computer (the Downloads folder is a great location).  Then start Quicken and do File->File Import->Web Connect, the rest of the process is the same as before.
If Quicken tries to create a new account, try to change it to "link" to the existing account.  If that is not possible, cancel the download/import to prevent a new account from being created (if you "saved" the file, you won't have to download it again).  Quicken is not recognizing the FI information in the download as the same as the existing account, so it wants to create a new account.  

What you need to do is to disable One Step Update (OSU) on the existing account to make it available for "linking".  To disable OSU, go to the existing account's register and do a Ctrl+Shift+E.  This will take you to the Account Details window for the account.  Select the Online Services tab and then click on "disable" or "deactivate".  Once disabled, you can do the download again.  If you "saved", your download is still good, just do the import again.
After you have downloaded and accepted all of the historical data that you want or can get, you will need to activate OSU again if you had to de-activate it earlier.  That process is the same as before, but this time the button should say "activate" or "enable".

Now, there is one last thing you need to do, you need to change the Opening Balance transaction to compensate for the added history which was not taken into consideration when the account was originally created.  Find that transaction and change its date so that it is the oldest transaction in the register.  You will need to change the amount so that the new ending balance is the same as the one from before starting this process (remember, you recorded it somewhere).  Since by definition, the Opening Balance is a reconciled transaction whose category points back to the same account, Quicken will warn you about it.  In this instance, it is okay and you can ignore the warning.  It is probably the only time you can ignore a warning.
Now, with OSU re-activated and your Opening Balance transaction modified, you should be good to go.