Hello, newb here. Is it possible to use account credit to upgrade from S1 to S2?

It would be helpful if you could as I have enough account credit to upgrade my license.

What account credit? If u mean the credits system in S1, then that doesn't help you get s2 in any way.
But if you mean the account credits at lfsworld then you need to login at www.lfs.net an click on "Account Details" and there you should have the option to use the 12£ for purcasing S2.

shoot me if i'm wrong

I think the situation is more like - if user paid £15 for skin download or that SMS thingy and has £12 left, can that £12 be used to upgrade from S1 to S2? In any other situation, no!

Log in on the main LFS site, click on "Buy A License", read the text and if you have those £12 on your LFS account, you will see this text:

Quote from lfs.net :

Select your item from the list:
NOTE: because you have a positive credit on your account of £12 you can purchase an item directly using your LFS account credit. If you want to do that, please email us, stating what you want to buy.

OK, so I emailed them to ask to buy the license with my account credit and they activated it for me.

So, anyone else who wants to do the same, email the staff and they will use it to activate your license

Welcome to the wonderful world of S2