my server 2008 r2 is running slow .any maintenance tips or task to be done

we have window server 2008 r2 and hp thin clients connected to the server and now the rdp on the thin clients is slow. how to increase the performance of the server and thin clients and also when i checked with the task manager the ram is utlisized with full extent that is we have 2 gb ram for server full 1.98 gb is utilized as show in the graph.