Do not do this ( @oreo_muncher has 8sp Claris groupset). You can't just replace one thing with 105 'written' on it. Current 105 stuff is 11 speed. As others have said (with my additions) items needed will be: rear wheel (with 11sp freehub), cassette, chain, STIs, RD and FD, and chainset (and most likely BB too).when things start to wear out, replace them with 105
I'd be amazed to get that (105 STIs, cassette, chain, front and rear mechs) for £200 even to fit yourself @vickster .