Why do you want to upgrade?
What mod are you using now?
What tank are you using now?
What batteries do you have?
Do you have an external charger?
Are you a mouth to lung vaper (MTL) or direct lung (DL)?
Do you prefer something that'll easily fit in your pocket or are you ok with larger/bulkier mods?
Do you prefer just power/watt mode or are you more partial to temperature control (TC)?
Are you new to vaping, are you a veteran, or somewhere in between?
Unfortunately the question is too vague and difficult to answer without more info provided to direct us to assist.
Everyone likes something different.
I can certainly recommend about 60 different mods that I own that you may like but then again you may not like any of them.
Let us know what you're after and we can definitely provide some great feedback narrowing the field a bit.