When to file amendment (if it reduces my refund or has me paying IRS)?

Hello

 

Status of my original return:

- Waiting on Federal Tax Refund (looks it it may take several weeks or months)

- Received State Tax Refund

 

I will be getting a corrected W2 soon (4-6 weeks). It has a good potential to reduce my claimed refund (or worse, may have me paying the IRS/State). 

 

Should I wait for my Federal Tax Refund to file an amendment after I get the W2C or should I file immediately after I get W2C without waiting for the refund. 

 

I saw following on the IRS website:
 
"If you're filing an amended tax return to claim an additional refund, wait until you receive your original tax refund before filing Form 1040X. If you owe additional taxes with Form 1040X, pay the tax with the return or as soon as possible to minimize interest and penalties."