I am using WebClient,DownloadString(\"http://example.com/string.txt\"); When I call it the memory jumps up, but never goes down again, and since I need 2-3 different strings
"Memory usage" as displayed by tools like Taskmgr.exe or ProcExp.exe tells you squat about the actual memory in use by a program. When virtual memory is released by the garbage collector, the free space is almost never returned to the operating system. It gets added to a list of free blocks, ready for re-use by the next allocation. The odds that the free blocks coalesce back into a range of pages that can be freed are quite small.
This is never a real problem, this is virtual memory. Another way to make you feel good quickly is to minimize the main window of the program. That trims the working set, the amount of RAM in use.