In Axis upgrades happens two types:
If its same reward type like reward -> reward, cashback -> cashback, miles -> miles then
- same card account in CIBIL used (so, no impact to 7 years history with new card contributing that account)
If its different reward type like reward -> cashback, reward -> miles then
- its not actually an upgrade, its just having another card (new account in CIBIL and both cards simulataneously contributing their own accounts), each has their own history.
So, if you downgrade/upgrade to low fee card on same existing card do check whethr downgrade/upgrade has same reward structure or not else you'll have two cards and have to pay two annual fees.
Moreover, whats the next best card with you in terms of credit age? If its closely 6+ years then you can safely close this card. No impact to CBIL or age.
Update -
Standard Charted - 1 account for all cards
ICICI - 4 accounts (1-Amazon, 1-Gemstone Cards, 1-Cobranded, 1 -Emeralde)
AXIS - each card 1 account*
SBI - each card 1 account
AMEX - each card 1 account
BOB - each card 1 account
HDFC - each card 1 account
RBL - each card 1 account
INDUSIND - each card 1 account
KOTAK - each card 1 account
IDFC - 2 accounts (1-Core Cards, 1-Cobranded)
HSBC - each card 1 account
CITI - each card 1 account
YES - each card 1 account
AU - each card...