You can convert altcoin to bitcoin or vice versa with the help of alt coin trading site just like poloniex, bittrex and many more just go to one of that sites and sell you altcoin for bitcoin. Just a reminder it's better if don't sell your coins because their value is cheap because of the price of bitcoin.
Yes, you may convert alt-coin to bitcoins and vice versa. The point here is to buy altcoins when their prices are low and sell at high prices.
and you may get the benefit and profits.
Most of the people know this simple business rule of buying at low and selling at high but most of the people does not know the altcoin they are investing, will it price will rise in future or not and end up in a wrong investment.
The thing to look for is the Market cap of the Coin, which not many people know about. If the market cap of a coin is high, there is a lot of chance that this coin will give you benefit if you invest in it.