You might convert this HELOC to a conventional mortgage by apply for and getting approved for a new first mortgage. Getting a new first mortgage would pay off the existing HELOC. If you don't want any cash out at your refinance then you are looking for a rate and term refinance.
There might be a problem with the loan amount as most lenders would want a higher loan amount.
The best thing to do is apply for a rate and term refinance, with the low loan amount you might have to take some money out as a cash our refinance.
When you speak with a loan consultant ask if they have mortgage program for low loan amounts such as the $50,000 loan amount that you have. With fees,point and other closing cost your loan amount would be approximately $52,000 to perhaps $53,000 at closing.
I hope this has been of some benefits to you, good luck.