I have a boxed version of the 737-800NGX installed.

The operation center version page says that  the current version is 1.10.6461 and the available version is 1.20.8885.

There is a notification from which I can install a new update but when I click on Ok to install the update I just get a Dos window that flashes but nothing gets updated.

Thanks in advance

I believe you have to obtain a more recent version from where you purchased (Aerosoft?), and then with that more recent version the on line updating with the operations center will work for you.

2 hours ago, bob755 said:

There is a notification from which I can install a new update but when I click on Ok to install the update I just get a Dos window that flashes but nothing gets updated.

The updater can only handle aircraft that are so old. Yours is multiple years out of date. Update your boxed version to the latest boxed update at support.aerosoft.com. Then try the update.

I downloaded and installed the latest version from Aerosoft after uninstalling the old version and then installed the update. All seems ok.

Thanks

After the update I see that the tutorial flights such as "PMDG 737NGX Tutorial #2 EHAM-LOWI Before Approach.FLT" no longer appear in the list when loading a flight in FSX.

3 hours ago, bob755 said:

After the update I see that the tutorial flights such as "PMDG 737NGX Tutorial #2 EHAM-LOWI Before Approach.FLT" no longer appear in the list when loading a flight in FSX.

The update shouldn't delete things unless someone manually deleted things. Either way, they really aren't that necessary.