I am holding BTC from long time ago. And this time BTC going up can I sell now with this price? Or I can wait for more days?
Depends on when you bought, personally, I'd advise against selling BTC at any price without having to recoup your initial investment. However, it's also important to have an investment strategy before coming into crypto (hence it's a crucial beam in the DYOR maxim).
This year, among other things, one thing is for certain: Bitcoin halving; which may likely impact the price of Bitcoin. You don't want to be on the wrong side before or after the halving - that's for sure! But you can get more out of Bitcoin if you try one/more of these (disclaimer: just an idea, not investment advice):
For long-term hodling: Cost average works well the sell once you can get back capital (until you recoup your initial investment and start earning real profits, keep hodling).
For mid-term: Try trading. Learn all the trading strategies there is, start by investing small, and move up gradually. NEVER get GREEDY.
For short-term: I have no clue what to advise here, as timing is very important, and Bitcoin is very volatile.