Though it seems unintuitive, you should rationally ignore the past performance of this stock (including the fact that it's at its 52-week high) and focus exclusively on factors that you believe should affect it moving forward. If you think it's going to go up even further, more than the return on your other options for where to put the money, keep the stock. If you think it's peaked and will be going down, now's a good time to sell.
To put it another way: if you didn't already have this stock, would you buy it today?
Your choice is just about the same: you can choose between a sum of cash equal to the present market value of the shares, OR the shares. Which do you think is worth more?
You also mentioned that you only have 10 stocks in the portfolio. Some are probably a larger percentage than others, and this distribution may be different than what you want in your portfolio. It may be time to do some rebalancing, which could involve selling some shares where your position is too large (as a % of your portfolio) and using the proceeds toward one or more categories you're not as invested in as you would like to be. This might be a good opportunity to increase the diversity in your portfolio.
If part of your reward and motivation for trading is emotional, not purely financial, you could sell now, mark it as a "win," and move on to another opportunity. Trading based on emotions is not likely to optimize your future balance, but not everybody is into trading or money for money's sake. What's going to help you sleep better at night and help boost your quality of life? If holding the stock will make you stress and regret a missed opportunity if it goes down, and selling it will make you feel happy and confident even if it still goes up more (e.g. you interpret that as further confirming that you made a good pick in the first place), you might decide that the risk of suboptimal financial returns (from emotion-based trading) is acceptable.
As CQM points out, you could also set a trailing sell order to activate only when the stock is a certain percentage or dollar amount below whatever it peaks at between the time you set the order and the time it fires/expires; the activation price will rise with the stock and hold as it falls.