Help with Maintenance Issue

This is my first posting on this forum, so I hope it works fine.

Problems with gear shifting can generally relate to a few things:

1) physical condition of derialeur(s) and their adjustment.

2) physical condition of cable(s) and their adjustment

3) physical condition of cogs/chainrings as well as the chain.

From your brief decription, it's hard to work out what is wrong. However, it sounds like a need for readjustment of deraileurs/cables that are normally required especially with season changes. If mechanics at the bike shop are knowledgeable and experienced, the problem should be rectified easily.

If you have not mechanically damaged your deraileurs and/or cogs or chain, and if you really like to do it youself, I would suggest to get the literature (user manuals) for deraileurs first, and then undo your cables, clean and lubricate them, and set up your deraileurs following the manuals.

When I was building my last bike, all components (Shimano) came with useful manuals. Check if you can get them (or download them). Good Luck.